THE  IHIOUL  SERIES  OF  SliOiRI 


COMPRISES    STANDARD    WORKS 


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___________    _._. : >gV— HUNTING' 

TON'S  Fine  Arts-CHAMPLiN'*  Polities1  Economy— MANSFIELD'S  Government  Manual- AM»EN'S 
Ethics— BROOKS'  Manual  of  Devotion— TRACY'S  School  Record,  &c. 

The  Teacher's  Library  consists  of  over  30  volumes  of  strictly  professional  literature,  as  PAGE'S 
Theory  and  Practice— HOLBROOK'S  Normal  Methods— NORTHEND'S  Teacher's  Assistant,  Ac. 

A  DESCRIPTIVE  CATALOGUE  of  all  these   and  many  more  may  be  obtained  by  enclosing  a 
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111 


A.  3.  BARHES  &  COMPAIY, 

National  Educational  Publishers, 
&  113  WILLIAM  STREET,  NEW  YORTL 


/  1: 

THE  WORMAN  SERIES  IN  MODERN  LANGUAGE. 

A  COMPLETE  COURSE  IN  GERMAN. 

By  JAMES  H.  WORMAN,  AM. 

EMBRACING 

ELEMENTARY    GERMAN    G-RA3MMIAR, 

COMPLETE    OERIVLAIN'    <jR  AMM  AR,  » 

COLLEGE!  ATE    OERMAIN'    RE  AIDER, 
ELEMENTARY    GERMAIN"    READER, 

G-ERivEATsr  COPY-BOOKR,  GERMAN  ECHO. 

HISTORY*  OtB1  GERMAN  LITERATURE, 
GERMAN  ANID  ENGLISH 


I.  THE  GERMAN  GRAMMARS  of  Worman  are  widely  preferred  on  ac- 
count of  their  clear,  explicit  method  (on  the  conversation  plan),  introducing  a  system 
of  analogy  and  comparison  with  the  learners'  own  language  and  others  commonly 
studied. 

The  arts  of  speaking,  of  understanding  the  spoken  language,  and  of  correct  pronun- 
ciation, are  treated  with  great  success. 

The  new  classifications  of  nouns  and  of  irregular  verbs  are  of  great  value  to  the 
pupil.  The  use  of  heavy  type  to  indicate  etymological  changes,  is  new.  The  Vocabu- 
lary is  synonymical  —  also  a  new  feature. 

II.  WORMAN'S    GERMAN  REAJ)ER    contains   progressive    selections 
from  a  wide  range  of  the  very  beet  German  authors,  including  three  complete  plays, 
which  are  usually  purehased  in  separate  form  for  advanced  students  who  have  com- 
pleted the  ordinary  Header. 

It  has  Biographies  of  eminent  authors,  Notes  after  the  test,  References  to  all  Ger- 
man Grammars  in  common  use,  and  an  adequate  Vocabulary;  also,  Exercises  for 
translation  into  the  German. 

III.  WORMAN'S   GERMAN  ECHO  (Deutsches  Echo}    is    entirely  a  new 
thing  in  this  country.    It  presents  familiar  colloquial  exercises  without  translation, 
and  will  teach  fluent  conversation  in  a  few  months  of  diligent  study. 

No  other  method  will  ever  make  the  student  at  home  in  a  foreign  language.  By  this 
he  thinks  in,  as  well  as  speaks  it.  For  the  time  being  he  is  a  German  through  and 
through.  The  laborious  process  of  translating  his  thoughts  no  longer  impedes  free 
unembarrassed  utterance. 


1  01IAF8  COMPLETE  FRENCH  COURSE 


IS  INAUGURATED  BT 

O      IDE 


Or,  "  French  Echo  ;M  on  a  plan  identical  with  the  German  Echo  described  above. 
This  will  be  followed  in  due  course  by  the  other  volumes  of 


THE   IF-RE^CH   SERIES, 
TIZ.: 

A   COMPLETE  GRAMMAR,  \A    FRENCH    READER, 

Aif  ELEMENTARY  GRAMMA  R,\  A    FRENCH    LEXICON, 
A  HISTORY  OF  FRENCH  LITERATURE. 


WORMAN'S   WORKS 

are  adopted  as  last  as  published  by  many  of  the  best  institutions  of  the  country.    In 
completeness,  adaptation,  and  homogeneity  for  consistent  courses  of  instruction,  they 

are  simply 


o 


- 


FOURTEEN  WEEKS 


IN 


DESCRIPTOR 


BY 


J.  DORMAN   STEELE,  PH.D. 

AUTHOR  OF  THE  FOURTEEN-WEEKS  SERIES  IN  PHYSIOLOGY,  PHILOSOPHY, 
CHEMISTRY,  AND  GEOLOGY. 


"The  heavens  declare  the  glory  of  God;  and  the  firmament  showeth  his 
banny-work."  PSALM  xix,  1. 


.    S.    BARNES    &    COMPANY, 

NEW    YORK    AND    CHICAGO. 


GIFT  OF 


FOURTEEN  WEEKS'  COURSES 

I-S73 

NATURAL    SCIENCE, 

BY 

J.  DORMAN    STEELE,  A.M.,  Pn.D. 

Fourtee^  Weeks  iij  Natural  Philosophy,  .     .  $i.50 
Fourteeij  Weeks  i?(  C^er^by.,   .....    i.5o 

1  50 

•    J-5° 
Fourteeij  Weeks  iq  Hunjan  Physiology,  .     .    1.50 

A  Key,  containing  Answers  to  the  Questions 
and  Problems  in  Steele's  14  Weeks'  Courses,  1.50 

A   HISTORICAL  SERIES, 

on  the  plan  of  Steele's  14  Weeks  in  the  Sciences, 
inaugztrated  by 

^  Brief  History  of  %  United  States,     .    .    i.50 

The  publishers  of  this  volume  will  send  either  of  the  above  by 
mail,  post-paid,  on  receipt  of  the  price. 

The  same  publishers  also  offer  the  following  standard  scientific 
works,  being  more  extended  or  difficult  treatises  than  those  of 
Prof.  Steele,  though  still  of  Academic  grade. 

Peck's  Gaqot's  Natural  Philosophy,   .    .    .  1.75 

Porter's  Principles  of  Cfyerqistry,  ....  2.00 

Jarvis'  Physiology  aqd  Laws  of  FJealtfy      .  1.65 

Wood's  Botanist  aijd  Florist,   .....  2.50 

CfyanQbers'  Elenjeijts  of  Zoology,   ....  1.50 

tyclqtyre's  ^stroijomy  aijd  the  Globes,    .     .  1.50 

Page's  Elerqeqts  of  Geology,    .....  1.25 

Address  A.  S.  BARNES  &  CO., 

Educational  Publishers, 

NEW  YORK   OR  CHICAGO. 

ENTERED  according  to  Act  of  Congress,  in  the  year  1869,  by 

A.    S.    BARNES    &    CO., 
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Southern  District  of  New  York. 
STEELE'S  AST. 

EDUCATION  DGPT 


PREFACE. 


DURING  the  past  few  years  great  advances  have 
been  made  in  astronomical  science.  A  new  hori- 
zontal parallax  of  the  sun  has  been  established. 
This  has  materially  altered  the  estimated  distances, 
etc.,  of  the  planets.  The  sun  is  much  nearer  us  than 
we  supposed,  and  light  has  lost  a  little  of  its  wonder- 
ful velocity.  ,  Much  additional  information  has  been 
obtained  concerning  Meteors  and  Shooting  Stars. 
The  investigations  connected  with  Spectrum  Analy- 
sis have  been  especially  suggestive.  Thus  on  every 
hand  the  facts  of  Astronomy  have  been  accumulat- 
ing. As  yet,  however,  they  are  scattered  through 
many  expensive  foreign  works,  and  are  consequently 
beyond  the  reach  of  most  of  our  schools.  It  has 
been  the  aim  of  the  author  to  collect  in  this  little 
volume  the  most  interesting  features  of  these  larger 
works.  Believing  that  Natural  Science  is  full  of  fas- 
cination, he  has  sought  to  weave  the  story  of  those 
far-distant  worlds  into  a  form  that  may  attract  the 
attention  and  kindle  the  enthusiasm  of  the  pupil. 
The  work  is  not  written  for  the  information  of  scien- 
tific men,  but  for  the  inspiration  of  youth.  The 
pages  therefore  are  not  burdened  with  a  multitude 

924232 


6  PREFACE. 

of  figures  which  no  memory  could  possibly  retain, 
Mathematical  tables  and  data,  Questions  for  Re- 
view, and  also  a  Guide  to  the  Constellations,  are 
given  in  the  Appendix,  where  they  may  be  useful 
for  constant  reference. 

The  author  would  call  particular  attention  to  the 
method  of  classifying  the  measurements  of  Space, 
and  the  practical  treatment  of  the  subjects .  of 
Parallax,  Harvest  Moon,  Eclipses,  the  Seasons, 
Phases  of  the  Moon,  Time,  Nebular  Hypothesis, 
&c. 

To  teachers  heretofore  compelled  to  use  a  cum- 
bersome set  of  charts,  it  is  hoped  that  the  star  maps 
here  offered  will  present  a  welcome  substitute.  The 
geometrical  figures  showing  the  actual  appearance 
of  the  constellations,  will  relieve  the  mind  confused 
with  the  idea  of  numberless  rivers,  serpents,  and 
classical  heroes.  The  brightest  stars  only  are  given, 
since  in  practice  it  is  found  that  pupils  remember 
the  general  outlines  alone. 

Finally,  the  author  commits  this  little  work  to 
the  hands  of  the  young,  to  whose  instruction  he  has 
consecrated  the  energies  of  his  life,  in  the  earnest 
hope  that,  loving  Nature  in  all  her  varied  phases, 
they  may  come  to  understand  somewhat  of  the  wis- 
dom, power,  beneficence,  and  grandeur  displayed  i» 
the  Divine  harmony  of  the  Universe. 

"One  God,  one  law,  one  element, 

And  one  far-off  Divine  event 
To  which  the  whole  creation  moves." 


PREFACE. 

• 

The  following  works,  among  others,  have  been  freely 
suited  in  preparing  this  volume: 

The  Heavens Guillernin. 

Astronomy Chambers. 

Introduction  to  Astronomy Hind. 

Solar  System Hind. 

Popular  Astronomy Airy. 

Popular  Astronomy Arago. 

Astronomy Norton. 

Astronomy Robinson. 

Astronomy Loomis. 

Age  of  Fable Bulfiuch. 

Poetry  of  Science Hunt. 

Outlines  of  Astronomy Herschel. 

Popular  Astronomy Mitchell. 

Astronomy  and  Physics Whewell. 

Annual  of  Scientific  Discovery Kneeland. 

The  Chemical  News. 


PUBLISHERS'  NOTICE.— Teachers  will  find  in  each  edition  of 
this  Series  certain  changes ;  not  such,  however,  as  to  cause  any 
inconvenience  in  the  use  of  all  the  editions  in  the  same  class. 
These  are  to  be  considered,  not  as  corrections  of  errors,  but  as 
improvements  suggested  by  the  constant  advance  made  in  science, 
and  by  practical  work  in  the  school-room.  The  publishers  are 
determined  to  spare  no  expense  in  making  this  Series  increasing- 
ly worthy  of  the  unprecedented  success  it  has  attained. 


SUGGESTIONS  TO  TEACHERS. 


THIS  work  is  designed  to  be  recited  in  the  topical  method. 
On  naming  the  title  of  a  paragraph,  the  pupil  should  be  able  to 
draw  on  the  blackboard  the  diagram,  if  any  is  given,  and  state 
the  substance  of  what  is  contained  in  the  book.  It  will  be 
noticed  that  the  cyder  of  topics,  in  treating  of  the  planets  and 
also  of  the  constellations,  is  uniform.  If  a  portion  of  the  class 
write  their  topics  in  full  upon  the  blackboard,  it  will  be  found 
a  valuable  exercise  in  spelling,  punctuation,  and  composition. 
Eveiy  point  which  can  be  illustrated  in  the  heavens  should  be 
shown  to  the  class.  No  description  or  apparatus  can  equal  tho 
'reality  in  the  sky.  After  a  constellation  has  been  traced,  the 
pupil  should  be  practised  in  star-map  drawing.  Much  profit- 
able instruction  can  be  obtained  in  this  way.  For  the  pur- 
pose of  more  easily  finding  the  heavenly  bodies  at  any  time, 
WHITALL'S  MOVABLE  PLANISPHERE  is  of  great  service.  It 
may  be  procured  of  the  publishers  of  this  work.  "  Orreries 
are  of  little  account."  A  tellurian  is  invaluable  in  explaining 
Precession  of  the  Equinoxes,  Eclipses,  Phases  of  the  Moon,  etc. 
Messrs.  A.  S.  Barnes  &  Co.,  New  York  City,  furnish  a  good  instru- 
ment at  a  low  price.  The  article  on  "  Celestial  Measurements," 
near  the  close  of  the  work,  should  be  constantly  referred  to  dur- 
ing the  term.  In  the  figures,  the  right-hand  side  represents  the 
west  and  the  left-hand  the  east.  When  it  is  important  to  obtain 
this  idea  correctly,  the  book  should  be  held  up  toward  the  south- 
ern sky. 

Never  let  a  pupil  recite,  a  lesson,  nor  answer  a  question,  except 
it  be  a  mere  definition,  in  the  language  of  the  book,  Thje  text  is 
designed  to  interest  and  instruct  the  pupil ;  the  recitation  should 
afford  him  an  opportunity  of  expressing  what  he  has  learned,  in 
his  own  style  and  words. 


TABLE   OF   CONTENTS. 


CELESTIAL  MAP. 

I.    INTRODUCTION. 

PAG« 

HISTORY  OF  ASTRONOMY 16 

SPACE 35 

THE  THREE  SYSTEMS  OF  CIRCLES     .         .         .37 

II.    THE  SOLAR  SYSTEM    .        .        43 

THE  SUN 46 

THE  PLANETS 65 

VULCAN 82 

MERCURY     . 83 

VENUS 89 

THE  EARTH .96 

THE  SEASONS no 

PRECESSION  AND  NUTATION  .  .  .120 
REFRACTION,  ABERRATION  AND  PARALLAX  .  130 
THE  MOON  .  .  .  .  -139 

ECLIPSES 155 

THE  TIDES    .......       165 

MARS       .        .        . 168 

THE  MINOR  PLANETS         .        .        .        ,        .172 
JUPITER          ....  ...   175 

SATURN 182 

URANUS .189 

NEPTUNE 191 

METEORS  AND  SHOOTING  STARS        .  .   194 


12  TABLE   OF   CONTENTS. 

PAGI 

COMETS 206 

ZODIACAL  LIGHT 217 


III.    THE  SIDEREAL  SYSTEM  .       .       219 

THE  STARS 221 

THE  CONSTELLATIONS 234 

NORTHERN  CIRCUMPOLAR  CONSTELLATIONS  .  234 
EQUATORIAL  CONSTELLATIONS  .  .  .  .242 
SOUTHERN  CONSTELLATIONS  .  .  .  263 

DOUBLE  STARS,  COLORED  STARS,  VARIABLE 
STARS,  CLUSTERS,  MAGELLANIC  CLOUDS, 
NEBULA,  &C 265 

THE  MILKY  WAY  280 


THE  NEBULAR  HYPOTHESIS          .         .         .         .282 
CELESTIAL  CHEMISTRY.— SPECTRUM  ANALYSIS       284 

TIME .        .        .288 

CELESTIAL  MEASUREMENTS      .         .         .         .298 

APPENDIX 311 

TABLES 312 

QUESTIONS 315 

GUIDE  TO  THE  CONSTELLATIONS          .       .        .331 
INDEX.        .  335 


INTRODUCTION. 


ASTRONOMY  (astron,  a  star,  and  nomos,  a  law)  treats 
of  the  Heavenly  Bodies — the  sun,  nioon,  planets, 
stars,  and,  as  our  globe  itself  is  a  planet,  of  the 
earth  also.  It  is,  above  all  others,  a  science  that 
cultivates  the  powers  of  the  imagination.  Yet  all 
its  theories  and  distances  are  based  upon  the  most 
rigorous  mathematical  demonstrations.  Thus  the 
study  has  at  once  the  beauty  of  poetry  and  the  ex- 
actness of  Geometry. 

The  Appearance  of  the  Heavens  to  an  Observer. — 
The  great  dome  of  the  sky  filled  with  glittering 
stars  is  one  of  the  most  sublime  spectacles  in  nature. 
To  enjoy  this  fully,  a  night  must  be  chosen  when 
the  air  is  clear,  and  the  moon  is  absent.  "We  then 
gaze  upon  a  deep  blue,  an  immense  expanse  studded 
with  stars  of  varied  color  and  brilliancy.  Some 
shine  with  a  vivid  light,  perpetually  changing  and 
twinkling;  others,  more  constant,  beam  tranquilly 
and  softly  upon  us ;  while  many  just  tremble  into 
our  sight,  like  a  Avave  that,  struggling  to  reach  some 
far-off  land,  dies  as  it  touches  the  shore.  In  the 
presence  of  such  weird  and  wondrous  beauty,  the 


14  INTRODUCTION. 

tenderest  sentinients  of  the  heart  are  aroused — a 
feeling  of  awy  and  reverence,  of  softened  melan- 
choly 2aii'gled;w;ith  a-,  thought  of  God,  comes  over 
us,'  and  awakens  the  better  nature  within  us.  Those 
far-off  lights  seem  full  of  meaning  to  us,  could  we 
but  read  their  holy  message  ;  they  become  real  and 
sentient,  and,  like  the  soft  eyes  in  pictures,  look  lov- 
ingly and  inquiringly  upon  us.  We  come  into  com- 
munion with  another  life,  and  the  soul  asserts  its 
immortality  more  strongly  than  ever  before.  We 
are  humbled  as  we  gaze  upon  the  infinity  of  worlds, 
and  strive  to  comprehend  their  enormous  distances, 
their  magnificent  retinue  of  suns.  The  powers  of 
the  mind  are  aroused,  and  eager  questionings  crowd 
upon  us.  What  are  those  glittering  fires?  What 
their  distances  from  us  ?  Are  they  worlds  like  our 
own  ?  Do  living,  thinking  beings  dwell  upon  them  ? 
Are  they  carelessly  scattered  through  infinite  space, 
or  is  there  an  order  of  the  universe  ?  Can  we  ever 
hope  to  fathom  those  mysterious  depths,  or  are  they 
closed  to  us  forever  ?  Many  of  these  problems  have 
been  solved ;  others  yet  await  the  astronomer  whose 
keen  eye  shall  be  strong  enough  to  read  the  myste- 
rious scroll  of  the  heavens.  Two  hundred  genera- 
tions of  study  have  revealed  to  us  such  startling 
facts,  that  we  wonder  how  man  in  his  feebleness 
can  grasp  so  much,  see  so  far,  and  penetrate  so 
deeply  into  the  mysteries  of  the  universe.  Astron- 
omy has  measured  the  distance  of  many  of  the  stars, 
and  of  all  the  planets ;  computed  their  weight  and 


INTRODUCTION.  15 

size,  their  days,  years,  and  seasons,  with  many  ot 
their  physical  features ;  made  a  map  of  the  moon,  in 
some  respects  more  perfect  than  any  map  of  the 
earth ;  tracked  the  comers  in  their  immense  sidereal 
journeys,  marking  their  paths  to  a  nicety  of  which 
we  can  scarcely  conceive,  and  at  last  it  has  analyzed 
the  structure  of  the  sun  and  far-off  stars,  announ- 
cing the  very  elements  of  which  they  are  composed. 
Observing  for  several  evenings  those  stars  which 
shine  with  a  clear  distinct  light,  we  notice  that  they 
change  their  position  with  respect  to  the  others. 
They  are  therefore  called  "planets"  (literally,  wan- 
derers). Others  remain  immovable,  and  shine  with 
a  shifting,  twinkling  light.  They  are  termed  the 
"fixed  stars"  although  it  is  now  known  that  they 
also  are  in  motion — the  most  rapid  of  any  known 
even  to  Astronomy — but  through  such  immense  or- 
bits that  they  seem  to  us  stationary.  Then,  too, 
diagonally  girdling  the  heavens,  is  a  whitish,  vapory 
belt — the  Milky  Way.  This  is  composed  of  multi- 
tudes of  millions  of  suns — of  which  our  own  sun 
itself  is  one — so  far  removed  from  us  that  their  light 
mingles,  and  makes  only  a  fleecy  whiteness.  This 
magnificent  panorama  of  the  heavens  is  before  us, 
inviting  our  study,  and  waiting  to  make  kn«  wn  to  us 
the  grandest  revelations  of  science. 


16  INTRODUCTION. 


DESCRIPTIVE  ASTRONOMY. 


HISTOEY. 

ASTRONOMY  is  the  most  ancient  of  all  sciences. 
The  study  of  the  stars  is  doubtless  as  old  as  man 
himself,  and  hence  many  of  its  discoveries  date  back 
of  authentic  records,  amid  the  dim  mysteries  of  tra- 
dition. In  tracing  its  history,  we  shall  speak  only 
of  those  prominent  facts  which  will  best  enable  us  to 
understand  its  progress  and  glorious  achievements. 

THE  CHINESE. — This  people  boast  much  of  their 
astronomical  discoveries.  Indeed  their  emperor 
claims  a  celestial  ancestry,  and  styles  himself  "  Son 
of  the  Sun."  They  possess  an  account  of  a  conjunc- 
tion of  four  planets  and  the  moon,  which  must  have 
occurred  a  century  before  the  Flood.  They  have 
also  the  first  record  of  an  eclipse  of  the  sun,  which 
took  place  about  two  hundred  and  twenty  years*  after 
the  Deluge.  It  is  reported  that  one  of  their  kings, 
two  thousand  years  before  Christ,  put  to  death  the 
principal  officers  of  state  because  they  had  failed  to 
calculate  an  approaching  eclipse. 

*  October  13,  2127  B.  c. 


HISTORY.  17 

THE  CHALDEANS. — The  Chaldean  shepherds,  watch- 
ing their  flocks  by  night  under  the  open  sky,  could 
not  fail  to  become  familiar  with  many  of  the  move- 
ments of  the  heavenly  bodies.  When  Alexander 
took  Babylon,  two  centuries  before  Christ,  he  found 
in  that  city  a  record  of  their  observations  reaching 
back  about  nineteen  centuries,  or  nearly  to  the  con- 
fusion of  tongues  at  the  Tower  of  Babel.  The 
Chaldeans  divided  the  day  into  twelve  hours,  in- 
vented the  sun-dial,  and  also  discovered  the  "  Saros  " 
or  "Chaldean  Period,"  which  is  the  length  of  time 
in  which  the  eclipses  of  the  sun  and  moon  repeat 
themselves  in  the  same  order. 

THE  GRECIANS. — In  the  seventh  century  B.  c., 
Tholes,  noted  for  his  electrical  discoveries,  acquired 
much  renown,  and  established  the  first  school  of 
Astronomy  in  Greece.  He  taught  that  the  earth  is 
round,  and  that  the  moon  receives  her  light  from 
the  sun.  He  introduced  the  division  of  the  earth's 
surface  into  zones,  and  the  theory  of  the  obliquity 
of  the  ecliptic.  He  also  predicted  an  eclipse  of  the 
sun  which  is  memorable  in  ancient  history  as  having 
terminated  a  war  between  the  Medes  and  Lydians. 
These  nations  were  engaged  in  a  fierce  battle,  but 
the  awe  produced  by  the  darkening  of  the  sun  was 
so  great,  that  both  sides  threw  down  their  arms  and 
made  peace.  Thales  had  two  pupils,  Anaximander 
and  Anaxagoras.  The  first  of  these  taught  that  the 
stars  are  suns,  and  that  the  planets  are  inhabited. 
He  erected  the  first  sun-dial,  at  Sparta.  The  second 


18  INTRODUCTION. 

maintained  that  there  is  but  one  God,  that  the  sun 
is  solid,  and  as  large  as  the  country  of  Greece,  and 
attempted  to  explain  eclipses  and  other  celestial 
phenomena  by  natural  causes.  For  his  audacity 
and  impiety,  as  his  countryman  considered  it,  he 
and  his  family  were  doomed  to  perpetual  banish- 
ment. 

Pythagoras  founded  the  second  celebrated  astro- 
nomical school,  at  Crotona,  at  which  were  educated 
hundreds  of  enthusiastic  pupils.  He  knew  the 
causes  of  eclipses,  and  calculated  them  by  means  of 
the  Saros.  He  was  most  emphatically  a  dreamer. 
He  conceived  a  system  of  the  universe,  in  many  re- 
.  spects  correct ;  yet  he  advanced  no  proof,  and  made 
few  converts  to  his  views,  and  they  were  soon  well- 
nigh  forgoften.  He  held  that  the  sun  is  the  centre 
of  the  solar  system,  and  that  the  planets  revolve 
about  it  in  circular  orbits ;  that  the  earth  revolves 
daily  on  its  axis,  and  yearly  around  the  sun ;  that 
Venus  is  both  morning  and  evening  star ;  that  the 
planets  are  inhabited — and  he  even  attempted  to 
calculate  the  size  of  some  of  the  animals  in  the 
moon ;  that  the  planets  are  placed  at  intervals  cor- 
responding to  the  scale  in  music,  and  that  they  move 
in  harmony,  making  the  "music  of  the  spheres," 
but  that  this  celestial  concert  is  heard  only  by  the 
gods — the  ears  of  man  being  too  gross  for  such 
divine  melody. 

^      Eudoxus,  who  lived  in  the  fourth  century  B.  c.,  in- 
vented the  theory  of  the  Crystalline  Spheres.     He 


HISTORY.  19 

held  that  the  heavenly  bodies  are  set,  like  gems,  in 
hollow,  transparent,  crystal  globes,  which  are  so 
pure  that  they  do  not  obstruct  our  view,  while  they 
all  revolve  around  the  earth.  The  planets  are 
placed  in  one  globe,  but  have  a  power  of  moving 
themselves,  under  the  guidance — as  Aristotle  taught 
— of  a  tutelary  genius,  who  resides  in  each,  and 
rules  over  it  as  the  mind  rules  ove**  the  body. 

Hipparclms,  who  flourished  in  the  second  century 
B.  c.,  has  been  called  the  "  Newton  of  Antiquity." 
He  was  the  most  celebrated  of  the  Greek  astrono- 
mers. He  calculated  the  length  of  the  year  to  with- 
in six  minutes,  discovered  the  precession  of  the  equi- 
noxes, and  made  the  first  catalogue  of  the  stars — 
1081  in  number. 

THE  EGYPTIANS. — Egypt,  as  well  as  Chaldea,  was 
noted  for  its  knowledge  of  the  sciences  long  before 
they  were  cultivated  in  Greece.  It  was  the  practice 
of  the  Greek  philosophers,  before  aspiring  to  the 
rank  of  teacher,  to  travel  for  years  through  these 
countries,  and  gather  wisdom  at  its  fountain-head. 
Pythagoras  spent  thirty  years  in  this  manner.  Two 
hundred  years  after  Pythagoras,  the  celebrated 
school  of  Alexandria  was  established.  Here  were 
concentrated  in  vast  libraries  and  princely  halls 
nearly  all  the  wisdom  and  learning  of  the  world. 
Here  flourished  all  the  sciences  and  arts,  under  the 
patronage  of  munificent  kings.  At  this  school  Ptol- 
emy, a  Grecian,  wrote  his  great  work,  the  "Alma- 
gest," which  for  fourteen  centuries  was  the  text- 


20  INTRODUCTION. 

book  of  astronomers.  In  this  work  was  given  what 
is  known  as  the  "Ptolemaic  System."  It  was 
founded  largely  upon  the  materials  gathered  by 
previous  astronomers,  such  as  Hipparchus,  whom 
we  have  already  mentioned,  and  Eratosthenes,  who 
computed  the  size  of  the  earth  by  the  means  even 
now  considered  the  best — the  measurement  of  an 
arc  of  the  meridian. 

PTOLEMAIC  THEORY. — The  movements  of  the  planets 
were  to  the  ancients  extremely  complex.  Venus,  for 
instance,  was  sometimes  seen  as  "  evening  star"  in 
the  west,  and  then  again  as  "  morning  star"  in  the 
east.  Sometimes  she  seemed  to  be  moving  in  the 
same  direction  as  the  sun,  then  going  apparently 
behind  the  sun,  appeared  to  pass  on  again  in  a 
course  directly  opposite.  At  one  time  she  would 
recede  from  the  sun  more  and  more  slowly  and 
coyly,  until  she  would  appear  to  be  entirely  station- 
ary; then  she  would  retrace  her  steps,  and  seem 
to  meet  the  sun.  All  these  facts  were  attempted 
to  be  accounted  for  by  an  incongruous  system  of 
"  cycles  and  epicycles,"  as  it  is  called.  The  advo- 
cates of  this  theory  assumed  that  every  planet  re- 
volves in  a  circle,  and  that  the  earth  is  the  fixed 
centre  around  which  the  sun  and  the  heavenly  bodies 
move.  They  then  conceived  that  a  bar,  or  some- 
thing equivalent,  is  connected  at  one  end  with  the 
earth ;  that  at  some  part  of  this  bar  the  sun  is  at- 
tached ;  while  between  that  and  the  earth, Venus  is 
fastened — not  to  the  bar  directly,  but  to  a  sort  of 


HISTORY.  21 

crank ;  and  further  on,  Mercury  is  hitched  on  in  the 
same  way.  In  the  cut,  let  A  be  the  earth,  S  the  sun, 
ABDF  the  bar  (real  or  imaginary),  BC  the  short 
bar  or  crank  to  which  Venus  is  tied,  D  E  another 
bar  for  Mercury,  F  G  another  bar,  with  still  another 
short  crank,  at  the  end  of  which,  H,  Mars  is  attached. 


THE  PTOLEMAIC  THEORY. 


Thus  they  had  a  complete  system.  They  did  not 
exactly  understand  the  nature  of  these  bars — 
whether  they  were  real  or  only  imaginary — but  they 
did  comprehend  their  action,  as  they  thought ;  and 
so  they  supposed  the  bar  revolved,  carrying  the  sun 
and  planets  along  in  a  large  circle  about  the  earth  ; 
while  all  the  short  cranks  kept  flying  around,  thus 
sweeping  each  planet  through  a  smaller  circle.  By 
this  theory,  we  can  see  that  the  planets  would 
sometimes  go  in  front  of  the  sun  and  sometimes 
behind;  and  their  places  were  so  accurately  pre- 
dicted, that  the  error  could  not  be  detected  by  the 
rude  instruments  then  in  use.  As  soon  as  a  new 
motion  of  one  of  the  heavenly  bodies  was  discov- 
ered, a  new  crank,  and  of  course  a  new  circle,  was 


22  INTRODUCTION. 

added  to  account  for  the  fact.  Thus  the  system 
became  more  and  more  complicated,  until  a  com- 
bination of  five  cranks  and  circles  was  necessary  to 
make  the  planet  Mars  keep  pace  with  the  Ptolemaic 
theory.  No  wonder  that  Alfonso,  king  of  Castile, 
and  a  very  celebrated  patron  of  Astronomy,  revolted 
at  the  cumbersome  machinery,  and  cried  out,  "If 
I  had  been  consulted  at  the  creation,  I  could  have 
done  the  thing  better  than  that !" 

ASTROLOGY. — After  the  death  of  Ptolemy,  Astron- 
omy ceased  to  be  cultivated  as  a  science.  The 
Romans,  engrossed  with  schemes  of  conquest,  never 
produced  a  single  great  astronomer.  Indeed,  when 
Julius  Caesar  reformed  the  calendar,  he  obtained  the 
assistance,  not  of  a  Roman,  but  of  Sosigenes  an  Alex- 
andrian. The  Arabians  studied  the  stars  merely  for 
purposes  of  soothsaying  and  prophecy.  They  pro- 
fessed to  foretell  the  future  by  the  appearance  of  the 
planets  or  stars.  All  of  the  ancient  astronomers 
shared  more  or  less  in  this  superstition.  Tiberius, 
emperor  of  Rome,  practised  Astrology.  Hippoc- 
rates himself,  the  "  Father  of  Medicine  "  who  flour- 
ished in  the  4th  century  B.  C.,  ranked  it  among  the 
most  important  branches  of  knowledge  for  the  phy- 
sician. Star-diviners  were  held  in  the  greatest 
estimation.  The  system  continued  to  increase  in 
credit  until  the  Middle  Ages,  when  it  was  at  its 
height  of  popularity.  The  issue  of  any  important 
undertaking,  or  the  fortunes  of  an  individual,  were 
foretold  by  the  astrologer,  who  drew  up  a  Horoscope, 


HISTORY.  23 

representing  the  position  of  the  stars  and  planets  at 
the  beginning  of  the  enterprise,  or  at  the  birth  of 
the  person.  It  was  a  complete  and  complicated 
system,  and  contained  regular  rules,  which  guided 
the  interpretation,  and  which  were  so  abstruse 
that  they  required  years  for  their  entire  mastery. 
Venus  foretold  love;  Mars,  war;  the  Pleiades,* 
storms  at  sea.  The  ignorant  were  not  alone  the 
dupes  of  this  visionary  system.  Lord  Bacon  be- 
lieved in  it  most  firmly.  As  late  even  as  the  reign 
of  Charles  II.,  Lilly,  a  famous  astrologer  of  that 
time,  was  called  before  a  committee  of  the  House  of 
Commons  to  give  his  opinion  on  the  probable  issue 
of  some  enterprise  then  under  consideration.  How- 
ever foolish  the  system  of  Astrology  itself  may  have 
been,  it  preserved  the  science  of  Astronomy  during 
the  Dark  Ages,  and  prompted  to  accurate  observa- 
tion and  diligent  study  of  the  heavens. 

THE  COPERNICAN  SYSTEM. — About  the  middle  of 
the  sixteenth  centta'y,  Copernicus,  breaking  uway 
from  the  theory  of  Ptolemy,  which  was  still  taught 
in  all  the  institutions  of  learning  in  Europe,  revived 
the  theory  of  Pythagoras.  He  saw  how  beautiful- 
ly simple  is  the  idea  of  considering  the  sun  the 
grand  centre  about  which  revolve  the  earth  and  all 
the  planets.  He  noticed  how  constantly,  when  we 
arc  riding  swiftly,  we  forget  our  own  motion,  and 
think  that  the  trees  and  fences  are  gliding  by  us  in 


*  Plc'-3\i-dcz. 


24  INTRODUCTION. 

the  contrary  direction.  He  applied  this  thought  to 
the  movements  of  the  heavenly  bodies,  and  main- 
tained that,  instead  of  all  the  starry  host  revolving 
about  the  earth  once  in  twenty-four  hours,  the  earth 
simply  turns  on  its  own  axis :  that  this  produces 
the  apparent  daily  revolution  of  the  sun  and  stars ; 
while  the  yearly  motion  of  the  earth  about  the  sun, 
transferred  in  the  same  manner  to  that  body,  would 
account  for  its  various  movements.  Though  Coper- 
nicus thus  •  simplified  so  greatly  the  Ptolemaic  the- 
ory, he  yet  found  that  the  idea  of  circular  orbits  for 
the  planets  would  not  explain  all  the  phenomena ; 
he  therefore  still  retained  the  "  cycles  and  epicycles" 
that  Alfonso  had  so  heartily  condemned.  For  forty 
years  this  illustrious  astronomer  carried  on  his  ob- 
servations in  the  upper  part  of  a  humble,  dilapi- 
dated farm-house,  through  the  roof  of  which  he  had 
an  unobstructed  view  of  the  sky.  The  work  con- 
taining his  theory  was  at  last  published  just  in  time 
to  be  laid  upon  his  death-bed. 

TYCHO  BEAHE,  a  celebrated  Danish  astronomer, 
next  propounded  a  modification  of  the  Copernican 
system.  He  rejected  the  idea  of  cycles  and  epi- 
cycles, but,  influenced  by  certain  passages  of  Scrip- 
ture, maintained,  with  Ptolemy,  that  the  earth  is  the 
centre,  and  that  all  the  heavenly  bodies  revolve 
about  it  daily  in  circular  orbits.  Brahe  was  a  noble- 
man of  wealth,  and,  in  addition,  received  large  sums 
from  the  Government.  He  erected  a  magnificent 
observatory,  and  made  many  beautiful  and  rare  in- 


HISTORY.  25 

struments.  Clad  in  his  robes  of  state,  he  watched 
the  heavens  with  the  intelligence  of  a  philosopher 
and  the  splendor  of  a  king.  His  indefatigable  in- 
dustry and  zeal  resulted  in  the  accumulation  of  a 
vast  fund  of  astronomical  knowledge,  which,  how- 
ever, he  lacked  the  wit  to  apply  to  any  further  ad- 
vance in  science.  His  pupil,  Kepler,  saw  these  facts, 
and  in  his  fruitful  mind  they  germinated  into  three 
great  truths,  called  Kepler's  laws.  These  constitute 
almost  the  sum  of  astronomical  knowledge,  and  form 
one  of  the  most  precious  conquests  of  the  human 
mind.  They  are  the  three  arches  of  the  bridge  over 
which  Astronomy  crossed  the  gulf  between  the  Ptol- 
emaic and  Copernican  systems. 

KEPLER'S  LAWS. — Kepler,  taking  the  investigations 
of  his  master,  Tycho  Brahe,  determined  to  find  what 
is  the  exact  shape  of  the  orbits  of  the  planets.  He 
adopted  the  Copernican  theory,  that  the  sun  is 
the  centre  of  the  system.  At  that  time  all  be- 
lieved the  orbits  to  be  circular.  Since,  as  they  said, 
the  circle  is  perfect,  is  the  most  beautiful  figure  in 
nature,  has  neither  beginning  nor  ending,  therefore 
it  is  the  only  form  worthy  of  God,  and  He  must 
have  used  it  for  the  orbits  of  the  worlds  He  has 
made.  Imbued  with  this  romantic  view,  Kepler 
commenced  with  a  rigorous  comparison  of  the 
places  of  the  planet  Mars,  as  observed  by  Brahe, 
with  the  places  as  stated  by  the  best  tables  that 
could  be  computed  on  the  circular  theory.  For  a 
time  they  agreed,  but  in  certain  portions  of  the 

2 


26 


INTRODUCTION. 


orbit  tlie  observations  of  Brahe  would  not  fit  tlie 
computed  place  by  eight  minutes  of  a  degree.  Be- 
lieving that  so  good  an  astronomer  could  not  be 
mistaken  as  to  the  facts,  Kepler  exclaimed,  "  Out  of 
these  eight  minutes  we  will  construct  a  new  theory 
that  will  explain  the  movements  of  all  planets."  He 
resumed  his  work,  and  for  eight  years  continued  to 
imagine  every  conceivable  hypothesis,  and  then  pa- 
tiently to  test  it — "hunt  it  down,"  as  he  called  it. 
Each  in  turn  proved  false,  until  nineteen  had  been 
tried.  He  then  determined  to  abandon  the  circle 
and  adopt  another  form.  The  ellipse  suggested  itself 
to  his  mind.  Let  us  see  how  this  figure  is  made. 


Attach  a  thread  to  two  pins,  as  at  F  F  in  the 
figure ;  next  move  a  pencil  along  with  the  thread, 
the  latter  being  kept  tightly  stretched,  and  the  point 
will  mark  a  curve  which  is  flattened  in  proportion 


HIHTOBY.  27 

to  the  length  of  the  string  we  use, — the  longer  the 
string,  the  nearer  a  circle  will  the  figure  become. 
This  figure  is  the  ellipse.  The  two  points  F  F  are 
called  the  foci  (singular,  focus).  We  can  now  under- 
stand Kepler's  attempt,  and  the  glorious  triumph 
which  crowned  his  seventeen  years  of  unflagging  toil. 

First  Law. — With  this  figure  he  constructed  an 
orbit,  having  the  sun  at  the  centre,  and  again  fol- 
lowed the  planet  Mars  in  its  course.  But  very  soon 
there  was  as  great  discrepancy  between  the  observed 
and  computed  places  as  before.  Undismayed  by 
this  failure,  Kepler  assumed  another  hypothesis. 
He  determined  to  place  the  sun  at  one  of  the  foci 
of  the  ellipse,  and  once  more  "hunted  down"  the 
theory.  For  a  whole  year  he  traced  the  planet 
along  the  imaginary  orbit,  and  it  did  not  diverge. 
The  truth  was  discovered  at  last,  and  Kepler  an- 
nounced his  first  great  law — 

PLANETS  BEVOLVE  IN  ELLIPSES,  WITH  THE  SUN  AT 
ONE  FOCUS. 

Second  Law. — Kepler  knew  that  the  planets  do 
not  move  with  equal  velocity  in.  the  different  parts 
of  their  orbits.  He  next  set  about  establish- 
ing some  law  by  which  this  speed  could  be  deter- 
mined, and  the  place  of  the  planet  computed.  He 
drew  an  ellipse,  and  marked  the  various  positions  of 
the  planet  Mars  once  more.  He  soon  found  that 
when  at  its  perihelion  (point  nearest  the  sun)  it 
moves  the  fastest,  but  when  at  its  aphelion  (point 
furthest  from  the  sun)  it  moves  the  slowest.  Once 


28  INTRODUCTION. 

more  he  "  hunted  down"  various  hypotheses,  until 
at  last  he  discovered  that  while  in  going  from  B  to 
A  the  planet  moves  very  slowly,  and  from  D  to  C 

Fig.  3. 


very  rapidly;  yet  the  space  inclosed  between  the 
lines  S  B  and  S  A  is  equal  to  that  inclosed  between 
S  D  and  S  C.  Hence  the  second  law — 

A  LINE  CONNECTING  THE  CENTRE  OF  THE  EARTH  WITH 
THE  CENTRE  OF  THE  SUN,  PASSES  OVER  EQUAL  SPACES  IN 
EQUAL  TIMES. 

Third  ,Laiv. — Kepler,  not  satisfied  with  the  dis- 
covery of  these  laws,  now  determined  to  ascertain 
if  there  were  not  some  relation  existing  between  the 
times  of  the  revolution  of  the  planets  about  the  sun 
and  their  distances  from  that  body.  With  the  same 
wonderful  patience,  he  took  the  figures  of  Tycho 
Brahe,  and  began  to  compare  them.  He  tried  them 
in  every  imaginable  relation.  Next  he  took  their 
squares,  then  he  attempted  their  cubes,  and  lastly 
he  combined  the  squares  and  the  cubes.  Here  was 
the  secret ;  but  he  toiled  around  it,  made  a  blunder, 


HISTORY.  29 

and  waited  for  months,  until,  once  more,  his  patience 
triumphed,  and  he  reached  the  third  law — 

THE  SQUARES  OF  THE  TIMES  OF  REVOLUTION  OF  THE 
PLANETS  ABOUT  THE  SUN,  ARE  PROPORTIONAL  TO  THE 
CUBES  OF  THEIR  MEAN  DISTANCES  FROM  THE  SUN.* 

In  rapture  over  the  discovery  of  these  three  laws, 
so  marked  by  that  divine  simplicity  which  pervades 
all  the  laws  of  nature,  Kepler  exclaimed,  "Nothing 
holds  me.  The  die  is  cast.  The  book  is  written,  to 
be  read  now  or  by  posterity,  I  care  not  which.  It 
may  well  wait  a  century  for  a  reader,  since  God  has 
waited  six  thousand  years  for  an  observer."f 

Galileo. — Contemporary  with  Kepler  was  the  great 
Florentine  philosopher,  Galileo.  He  discovered  the 
laws  of  the  pendulum  and  of  falling  bodies,  as  we 
have  already  learned  in  Natural  Philosophy.  He, 
however,  was  educated  in  and  believed  the  Ptolemaic 
theory.  A  disciple  of  the  Copernican  theory  hap- 
pening to  come  to  Pisa,  where  Galileo  was  teaching 

*  For  example :  The  square  of  Jupiter's  period  is  to  the  square 
of  Mars'  period,  as  the  cube  of  Jupiter's  distance  is  to  the  cube 
of  Mars'  distance ;  or,  representing  the  earth's  time  of  revolu- 
tion by  P,  and  her  distance  from  the  sun  by  p,  then  letting  D  and 
d  represent  the  same  in  another  planet,  we  have  the  proportion 
P2 :  D2  : :  p* :  d3 . 

f  Kepler,  strangely  enough,  believed  in  the  "  Music  of  the 
Spheres."  He  made  Saturn  and  Jupiter  take  the  bass,  Mars  the 
tenor,  Earth  and  Venus  the  counter,  and  Mercury  the  treble. 
This  shows  what  a  streak  of  folly  or  superstition  may  run 
through  the  character  of  the  noblest  man.  However,  as  John- 
son says,  a  mass  of  metal  may  be  gold,  though  there  be  in  it  a 
little  vein  of  tin. 


30  INTRODUCTION. 

as  professor  in  the  University,  drew  his  attention  to 
its  simplicity  and  beauty.  His  clear  discriminating 
mind  perceived  its  perfection,  and  he  henceforth 
advocated  it  with  all  the  ardor  of  his  unconquerable 
zeal.  Soon  after  he  learned  that  one  Jansen,  a  Dutch 
watchmaker,  had  invented  a  contrivance  for  making 
distant  objects  appear  near.  With  his  profound 
knowledge  of  optics  and  philosophical  instruments, 
Galileo  instantly  caught  the  idea,  and  soon  had  a 
telescope  completed  that  would  magnify  thirty  times. 
It  was  a  very  simple  affair — only  a  piece  of  lead 
pipe  with  glasses  set  at  each  end ;  but  it  was  the 
first  telescope  ever  made,  and  destined  to  over- 
throw the  old  Ptolemaic  theory,  and  revolutionize 
the  whole  science  of  Astronomy. 

Discoveries  made  ivith  the  telescope. — Galileo  now 
examined  the  moon.  He  saw  its  mountains  and  val- 
leys, and  watched  the  dense  shadows  sweep  over  its 
plains.  On  January  8, 1610,  he  turned  the  telescope 
toward  Jupiter.  Near  it  he  saw  three  bright  stars, 
as  he  considered  them,  which  were  invisible  to  the 
naked  eye.  The  next  night  he  noticed  that  those 
stars  had  changed  their  relative  positions.  Aston- 
ished and  perplexed,  he  waited  three  days  for  a  fair 
night  in  which  to  resume  his  observations.  The 
fourth  night  was  favorable,  and  he  again  found 
the  three  stars  had  shifted.  Night  after  night  he 
watched  them,  discovered  a  fourth  star,  and  finally 
found  that  they  were  all  rapidly  revolving  around 
Jupiter,  each  in  its  elliptical  orbit,  with  its  own  rate 


HISTORY.  31 

of  motion,  and  all  accompanying  the  planet  in  its 
journey  around  the  sun.  Here  \vas  a  miniature 
Copernican  system,  hung  up  in  the  sky  for  all  to  see 
and  examine  for  themselves. 

Reception  of  the  discoveries. — Galileo  met  with  the 
most  bitter  opposition.  Many  refused  to  look  through 
the  telescope  lest  they  might  become  victims  of  the 
philosopher's  magic.  Some  prated  of  the  wickedness 
of  digging  out  valleys  in  the  fair  face  of  the  moon. 
Others  doggedly  clung  to  the  theory  they  had  held 
from  their  youth  up.  As  a  specimen  of  the  arguments 
adduced  against  the  new  system,  the  following  by 
Sizzi  is  a  fair  instance.  "  There  are  seven  windows 
in  the  head,  through  which  the  air  is  admitted  to  the 
body,  to  enlighten,  to  warm,  and  to  nourish  it, — two 
nostrils,  two  eyes,  two  ears,  and  one  mouth.  So  in 
the  heavens  there  are  two  favorable  stars,  Jupiter  and 
Venus ;  two  unpropitious,  Mars  and  Saturn ;  two 
luminaries,  the  Sun  and  Moon  ;  and  Mercury  alone, 
undecided  and  indifferent.  From  which,  and  from 
many  other  phenomena  of  Nature,  such  as  the  seven 
metals,  etc.,  we  gather  that  the  number  of  planets  is 
necessarily  seven.  Moreover,  the  satellites  are  in- 
visible to  the  naked  eye,  can  exercise  no  influence 
over  the  earth,  and  would  be  useless,  and  therefore 
do  not  exist.  Besides,  the  week  is  divided  into  seven 
days,  which  are  named  from  the  seven  planets.  Now, 
if  we  increase  the  number  of  planets,  this  whole 
system  falls  to  the  ground." 

NEWTON. — As  we  have  seen,  the  truth  of  the  Co- 


32  INTKODUCTION. 

pernican  system  was  fully  established  by  the  discov- 
eries of  Galileo  with  his  telescope.  Philosophers 
gradually  adopted  this  view,  and  the  Ptolemaic 
theory  became  a  relic  of  the  past.  In  1666,  Newton, 
a  young  man  of  twenty-four  years,  was  spending  a 
season  in  the  country,  on  account  of  the  plague 
which  prevailed  at  Cambridge,  his  place  of  resi- 
dence. One  day,  while  sitting  in  a  garden,  an  apple 
chanced  to  fall  to  the  ground  near  him.  Reflecting 
upon  the  strange  power  that  causes  all  bodies  thus 
to  descend  to  the  earth,  and  remembering  that  this 
force  continues,  even  when  we  ascend  to  the  tops  of 
high  mountains,  the  thought  occurred  to  his  mind, 
' '  May  not  this  same  force  extend  to  a  great  distance 
out  in  space  ?  Does  it  not  reach  the  moon  ?" 

Laws  of  Motion. — To  understand  the  philosophy 
of  the  reasoning  that  now  occupied  the  mind  of 
Newton,  let  us  apply  the  laws  of  motion  as  we  have 
learned  them  in  Philosophy.  When  a  body  is  once 
set  in  motion,  it  will  continue  to  move  forever  in  a 
straight  line,  unless  another  force  is  applied.  As 
there  is  no  friction  in  space,  the  planets  do  not  lose 
any  of  their  original  velocity,  but  move  now  with  the 
same  speed  which  they  received  in  the  beginning 
from  the  Divine  hand.  But  this  would  make  them 
all  pass  through  straight,  and  not  circular  orbits. 
What  causes  the  curve?  Obviously  another  force. 
For  example  :  I.  throw  a  stone  into  the  air.  It 
moves  not  in  a  straight  line,  but  in  a  curve,  because 
the  earth  constantly  bends  it  downward. 


HISTORY.  33 

Application.— Just  so  the  moon  is  moving  around 
the  earth,  not  in  a  straight  line,  but  in  a  curve.  Can 
it  not  be  that  the  earth  bends  it  downward,  just  as 
it  does  the  stone  ?  Newton  knew  that  a  stone  falls 
toward  the  earth  sixteen  feet  the  first  second.  He 
imagined,  after  a  careful  study  of  Kepler's  laws, 
that  the  attraction  of  the  earth  diminishes  according 
to  the  square  of  the  distance.  He  knew  (according 
to  the  measurement  then  received)  that  a  body  on 
the  surface  of  the  earth  is  four  thousand  miles  from 
the  centre.  He  applied  this  imaginary  law.  Sup- 
pose it  is  removed  four  thousand  miles  from  the 
surface  of  the  earth,  or  eight  thousand  miles  from 
the  centre.  Then,  as  it  is  twice  as  far  from  the 
centre,  its  weight  will  be  diminished  22,  or  4  times. 
If  it  were  placed  3,  4,  5,  10  times  further  away,  its 
weight  would  then  decrease  9,  16,  25,  100  times. 
If,  then,  the  stone  at  the  surface  of  the  earth  (four 
thousand  miles  from  the  centre)  falls  sixteen  feet 
the  first  second,  at  eight  thousand  miles  it  would 
fall  only  four  feet ;  at  240,000  miles,  or  the  distance 
of  the  moon,  it  would  fall  only  about  one-twentieth 
of  an  inch  (exactly  .053).  Now  the  question  arose, 
"  How  far  does  the  moon  fall  toward  the  earth,  i.  e., 
bend  from  a  straight  line,  every  second  ?"  For  sev- 
enteen years,  with  a  patience  rivalling  Kepler's,  this 
philosopher  toiled  over  interminable  columns  of  fig- 
ures to  find  how  much  the  moon's  path  around  the 
earth  curves  each  second.  He  reached  the  result 
at  last.  It  was  nearly,  but  not  quite  exact.  Disap- 


34  INTRODUCTION. 

pointed,  he  laid  aside  his  calculations.  Repeatedly 
he  reviewed  them,  but  could  not  find  a  mistake.  At 
length,  while  in  London,  he  learned  of  a  new  and 
more  accurate  measurement  of  the  distance  from  the 
circumference  to  the  centre  of  the  earth.  He  has- 
tened home,  inserted  this  new  value  in  his  calcula- 
tions, and  soon  found  that  the  result  would  be  cor- 
rect. Overpowered  by  the  thought  of  the  grand 
truth  just  before  him,  his  hand  faltered,  and  he 
called  upon  a  friend  to  complete  the  computation. 

From  the  moon,  Newton  passed  on  to  the  other 
heavenly  bodies,  calculating  and  testing  their  orbits. 
At  last  he  turned  his  attention  to  the  sun,  and,  by 
reasoning  equally  conclusive,  proved  that  the  attrac- 
tion of  that  great  central  orb  compels  all  the  planets 
to  revolve  about  it  in  elliptical  orbits,  and  holds 
them  with  an  irresistible  power  in  their  appointed 
paths.  At  last  he  announced  this  grand  Law  of 
Gravitation  : 

EVERY  PARTICLE  OF  MATTER  IN  THE  UNIVERSE  AT- 
TRACTS EVERY  OTHER  PARTICLE  OF  MATTER  WITH  A 
FORCE  DIRECTLY  PROPORTIONAL  TO  ITS  QUANTITY  OF 
MATTER,  AND  DECREASING  AS  THE  SQUARE  OF  THE  DIS- 
TANCE INCREASES. 


SPACE.  35 


SPACE. 

We  now  in  imagination  pass  into  space,  which 
stretches  out  in  every  direction  without  bounds  or 
measures.  We  look  up  to  the  heavens  and  try  to 
locate  some  object  among  the  mazes  of  the  stars, 
We  are  bewildered,  and  immediately  feel  the  neces- 
sity of  some  system  of  measurement.  Let  us  try  to 
understand  the  one  adopted  by  astronomers. 

THE  CELESTIAL  SPHERE. — The  blue  arch  of  the  sky, 
as  it  appears  to  be  spread  above  us,  is  termed  the 
Celestial  Sphere.  There  are  two  points  to  be  no- 
ticed here.  First,  that  so  far  distant  is  this  imagi- 
nary arch  from  us,  that  if  any  two  parallel  lines  from 
different  parts  of  the  earth  are  drawn  to  this  sphere, 
they  will  apparently  intersect.  Of  course  this  can- 
not be  the  fact ;  but  the  distance  is  so  immense,  that 
we  are  unable  to  distinguish  the  little  difference  of 
four  or  even  eight  thousand  miles,  and  the  two  lines 
will  seem  to  unite :  so  we  must  consider  this  great 
earth  as  a  mere  speck  or  point  at  the  centre  of  the 
Celestial  Sphere.  Second,  that  we  must  even  neg- 
lect the  entire  diameter  of  the  earth's  orbit,  so  that 
if  we  should  draw  two  parallel  lines,  one  from  each 
end  of  the  earth's  orbit,  to  the  sphere,  although 
these  lines  would  be  183,000,000  miles  apart,  yet 
they  would  be  extended  so  far  that  we  could  not 
separate  them,  and  they  would  appear  to  pierce  the 
sphere  at  the  same  point ;  which  is  to  say,  that  at 


\ 


36  INTRODUCTION. 

that  enormous  distance,  183,000,000  miles  shrink  to 
a  point.  Consequently,  in  all  parts  of  the  earth,  and 
in  every  part  of  the  earth's  orbit,  we  see  the  fixed 
stars  in  the  same  place.  This  sphere  of  stars  sur- 
rounds the  earth  on  every  side.  In  the  daytime  we 
cannot  see  the  stars  because  of  the  superior  light  of 
the  sun ;  but  with  a  telescope  they  can  be  traced, 
and  an  astronomer  will  find  certain  stars  as  well  at 
noon  as  at  midnight.  Indeed,  when  looking  at  the 
sky  from  the  bottom  of  a  deep  well  or  lofty  chimney, 
if  a  bright  star  happens  to  be  directly  overhead,  it 
can  be  seen  with  the  naked  eye  even  at  midday.  In 
this  way  it  is  said  a  celebrated  optician  was  first  led 
to  think  of  there  being  stars  by  day  as  well  as  by 
night.  One  half  of  the  sphere  is  constantly  visible 
to  us ;  and  so  far  distant  are  the  stars,  that  we  see 
just  as  much  of  the  sphere  as  we  would  if  the  upper 
part  of  the  earth  were  removed,  and  we  were  to 
stand  four  thousand  miles  further  away,  or  at  the 
very  centre  of  the  earth,  where  our  view  would  be 
bounded  by  a  great  circle  of  the  earth.  On  the  con- 
cave surface  of  the  celestial  sphere  there  are  imag- 
ined to  be  drawn  three  systems  of  circles :  the  HORI- 
ZON, the  EQUINOCTIAL,  and  the  ECLIPTIC  Systems. 
Each  of  these  has  (1)  its  Principal  Circle,  (2)  its 
Subordinate  Circles,  (3)  its  Points,  and  (4)  its  Meas- 


SPACE.  37 

I.  THE  HORIZON  SYSTEM. 

(a)  The  PRINCIPAL  CIKCLE  is  the  Rational  Horizon. 
This  is  the  great  circle  that,  passing  through  the 
centre  of  the  earth,  separates  the  visible  from  the 
invisible  heavens.     The  Sensible  Horizon  is  the  small 

1  circle  where  the  earth  and  sky  seem  to  meet ;  it  is 
parallel  to  the  rational  horizon,  but  distant  from  it 
the  semi-diameter  of  the  earth.  No  two  places  have 
the  same  sensible  horizon  :  any  two  on  opposite 
sides  of  the  earth  have  the  same  rational  horizon. 

(b)  THE-  SUBOEDINATE    CIRCLES. — These   are   the 
Prime  Vertical  circle  and  the  Meridian.     A  vertical 
Circle  is  one  passing  through  the  poles  of  the  horizon 

the  zenith  and  nadir).     The  Prime  Vertical  is  a 
*  ertical  circle  passing  through  the  East  and  West 
points.      The  Meridian  is  a  vertical  circle  passing 
hrough  the  North  and  South  points. 

(c)  POINTS.— These  are  the  Zenith,  the  Nadir,  the 
N.,  S.,  E.,  and  W.  points.     The  Zenith  is  the  point 
"lirectly  overhead,  and  the  Nadir  the  one  directly 
Underfoot.     They  are  also  the  poles  of  the  horizon 
— i.  e.,  the  points  where   the   axis   of  the   horizon 
pierces  fche  celestial  sphere.     The  N.,  S.,  E.,  and  W. 
points  are  familiar  to  all. 

(d)  MEASUREMENTS. — These  are  Azimuth,  Ampli- 
tude, Altitude,  and  Zenith  distance. 

Azimuth  is  the  distance  from  the  meridian,  meas- 
ured East  or  "West,  on  the  horizon  (to  a  vertical 
circle  passing  through  the  object). 


38  INTRODUCTION. 

Amplitude  (the  complement  of  Azimuth)  is  the 
distance  from  the  Prime  Vertical,  measured  on  the 
horizon,  North  or  South. 

Altitude  is  the  distance  from  the  horizon,  meas- 
ured on  a  vertical  circle  toward  the  zenith. 

Zenith  distance  (the  complement  of  Altitude)  is  the 
distance  from  the  zenith,  measured  on  a  vertical 
circle,  toward  the  horizon. 

The  Horizon  System  is  the  one  commonly  used 
in  observations  with  Mural  Circles  and  Transit  In- 
struments. 


IE.  THE  EQUINOCTIAL  SYSTEM. 

(a)  The  PRINCIPAL  CIRCLE  is  the  Equinoctial.    This 
is  the  Celestial  Equator,  or  the  earth's  equator,  ex- 
tended to  the  Celestial  Sphere. 

(b)  SUBORDINATE   CIRCLES. — These  are  the  Hour 
Circles  (Right  Ascension  Meridians)  and  the  Decli- 
nation Parallels.     The  Hour   Circles   are  thus  lo- 
cated.    The  Equinoctial  is  divided  into  360°,  equal 
to  twenty-four  hours  of  motion — thus  making  15° 
equal  to  one  hour  of  motion.     Through  these  divi- 
sions run  twenty-four  meridians,  each  constituting 
an  hour  of  motion  (time)  or  15°  of   space.     The 
Hoar  Circles  may  be  conceived  as  meridians  of  ter- 
restrial longitude  (15°  apart)  extended  to  the  Celes- 
tial Sphere.     (See  Colures,  p.  40.) 

The  Declination  Parallels  are  small   circles  par- 
allel to  the  Equinoctial ;  or  they  may  be  conceived 


SPACE.  39 

as  the  parallels  of  terrestrial  latitude  extended  to 
the  Celestial  Sphere. 

(c)  The  POINTS   are  the  Celestial  Poles   and  the 
Equinoxes.     The  Celestial  Poles  are  the  points  where 
the  axis  of  the  earth  extended  pierces  the  Celestial 
Sphere,  and  are  the  extremities  of  the  celestial  axis, 
just  as  the  poles  of  the  earth  are  the  extremities  of 
the  earth's  axis.     The  North  Point  is  marked  very 
nearly  by  the  North  Star,  and  every  direction  from 
that  is  reckoned  South,  and  every  direction  toward 
that  is  reckoned  North,  however  it  may  conflict  with 
our  ideas  of  the  points  of  the  compass. 

The  Equinoxes  are  the  points  where  the  Equi- 
noctial and  the  Ecliptic  (the  sun's  apparent  path 
through  the  heavens)  intersect. 

(d)  The  MEASUKEMENTS  are  Eight  Ascension  (B.  A.), 
Declination,  and  Polar  Distance. 

Hight  Ascension  is  distance  from  the  Vernal  Equi- 
nox, measured  on  the  equinoctial  eastward.  B.  A. 
corresponds  to  terrestrial  longitude,  and  may  ex- 
tend to  360°  East,  instead  of  180°  as  on  the  earth. 
E.  A.  is  never  measured  westward.  The  starting 
point  is  the  meridian  passing  through  the  vernal 
equinox;  as  the  meridian  passing  through  Green- 
wich is  the  point  from  which  terrestrial  longitude 
is  measured. 

Declination  is  distance  from  the  equinoctial,  meas- 
ured on  any  vertical  circle  or  meridian  North  or 
South.  It  corresponds  to  terrestrial  latitude. 

Polar  distance  (the  complement  of  Declination)  is 


4:0  INTRODUCTION. 

the  distance  from  the  Pole,  measured  on  a  vertical 
circle. 

The  Equinoctial  System  is  largely  used  by  modern 
astronomers.,  and  accompanies  the  Equatorial  Tele- 
scope, Sidereal  Clock,  and  Chronographs  of  the  best 
Observatories. 


III.  THE  ECLIPTIC  SYSTEM. 

(a)  The  PKINCIPAL  CIRCLE  is  the  Ecliptic.  This  is 
the  earth's  orbit  about  the  sun,  or  the  apparent 
path  of  the  sun  in  the  heavens.  It  is  inclined  to 
the  equinoctial  23°  28',  which  measures  the  inclina- 
tion of  the  Earth's  Equator  to  its  orbit,  and  is  called 
the  obliquity  of  the  ecliptic. 

(6)  The  SUBORDINATE  CIRCLES  are  Circles  of  Celestial 
Longitude,  the  Colures,  and  Parallels  of  Celestial 
Latitude. 

The  Circles  of  Celestial  Longitude  are  now  less 
employed.  They  are  measured  on  the  Ecliptic,  as 
circles  of  Bight  Ascension  (E.  A.)  are  now  measured 
on  the  Equinoctial. 

The  Colures  are  two  principal  meridians ;  the 
Equinoctial  Colure  is  the  meridian  passing  through 
the  equinoxes ;  the  Solstitial  Colure  is  the  meridian 
passing  through  the  solstitial  points. 

The  Parallels  of  Celestial  Latitude  are  now  little 
used,  but  are  small  circles  drawn  parallel  to  the 
ecliptic,  as  parallels  of  declination  are  now  drawn 
parallel  to  the  equinoctial. 


SPACE.  41 

(c)  The  POINTS  are  the  Poles  of  the  Ecliptic,  the 
Equinoxes,  and  the  Solstices. 

The  Poles  of  the  Ecliptic  are  the  points  where  the 
axis  of  the  earth's  orbit  meets  the  Celestial  Sphere. 
(Little  used.) 

The  Equinoxes  are  the  points  where  the  ecliptic 
intersects  the  equinoctial.  The  place  where  the 
sun  crosses  the  equinoctial*  in  going  North,  which 
occurs  about  the  21st  of  March,  is  called  the  Vernal 
Equinox.  The  place  where  the  sun  crosses  the 
equinoctial  in  going  South,  which  occurs  about  the 
21st  of  September,  is  called  the  Autumnal  Equinox. 
The  Solstices  are  the  two  points  of  "the  ecliptic  most 
distant  from  the  Equator ;  or  they  may  be  con- 
sidered to  mark  the  sun's  furthest  declination,  North 
and  South  of  the  equinoctial.  The  Summer  Sol- 
stice occurs  about  the  22d  of  June ;  the  Winter  Sol- 
stice occurs  about  the  22d  of  December. 

(d)  The  MEASUREMENTS  are  celestial  longitude  and 
latitude. 

Celestial  longitude  is  distance  from  the  Vernal  Equi- 
nox measured  on  the  ecliptic,  eastward. 

Celestial  latitude  is  distance  from  the  ecliptic  meas- 
ured on  a  Subordinate  circle,  north  or  south. 

THE  ZODIAC. 

A  belt  of  the  Celestial  Sphere,  8°  on  each  side  of 
the  ecliptic,  is  styled  the 'Zodiac.  This  is  of  very 

»  "  This  is  what  is  commonly  called  "  crossing  the  line." 


42  INTRODUCTION. 

high  antiquity,  having  been  in  use  among  the  an- 
cient Hindoos  and  Egyptians.  The  Zodiac  is  di- 
vided into  twelve  equal  parts — of  30°  each — called 
Signs,  to  each  of  which  a  fanciful  name  is  given. 
The  following  are  the  names  of  the 

SIGNS  or  THE  ZODIAC. 


Aries T 

Taurus « 

Gemini n 

Cancer © 

Leo si 

Virgo m 


Libra ^ 

Scorpio TTL 

Sagittarius * 

Capricornus V3 

Aquarius ^ 

Pisces  . ,  .  ^ 


"The  first,  T,  indicates  the  horns  of  the  Earn; 
the  second,  » ,  the  head  and  horns  of  the  Bull ;  the 
barb  attached  to  a  sort  of  letter  m,  designates  the 
Scorpion ;  the  arrow,  # ,  sufficiently  points  to  Sagit- 
tarius ;  v3  is  formed  from  the  Greek  letters  <rp,  the 
two  first  letters  of  rpfyos,  a  goat.  Finally,  a  bal- 
ance, the  flowing  of  water,  and  two  fishes,  tied  by 
a  string,  may  be  imagined  in  =^,  ^r,  and  x,  the  signs 
of  Libra,  Aquarius,  and  Pisces." 


She   Sdar   SjjBtem. 

In  them  hath  He  set  a  tabernacle  for  the  sun." 

PSALM  xix  4. 


THE    SOLAR    SYSTEM. 


THE  Solar  System  is  mainly  comprised  within  the 
limits  of  the  Zodiac.  It  consists  of — 

1.  The  Sun — the  centre." 

2.  The  major  planets — Vulcan  (undetermined),  Mercury, 

Venus,  Earth,  Mars,  Jupiter,  Saturn,  Uranus,  Neptune. 

3.  The  minor  planets,  at  present  one  hundred  and  seventeen 

in  number.    (The  paths  of  some  extend  a  little  outside 
the  Zodiac.) 

4  The  satellites  or  moons,  eighteen  in  number,  which  re- 
volve around  the  different  planets. 

5.  Meteors  and  shooting-stars. 

6.  Nine  comets  whose  orbits  have  been  computed,  and 

over  two  hundred  of  which  little  is  known. 

7.  The  Zodiacal  Light. 

HOW  WE  AKE  TO  IMAGINE  THE  SOLAR  SYSTEM  TO  OUR- 
SELVES.— We  are  to  think  of  it  as  suspended  in 
space ;  being  held  up,  not  by  any  visible  object,  but 
in  accordance  with  the  law  of  Universal  Gravitation 
discovered  by  Newton,  whereby  each  planet  attracts 
every  other  planet  and  is  in  turn  attracted  by  alL 
First,  the  Sun,  a  great  central  globe,  so  vast  as 
to  overcome  the  attraction  of  all  the  planets,  and 
compel  them  to  circle  around  him ;  next,  the  planets, 
each  turning  on  its  axis  while  it  flies  around  the 


46  THE   SOLAB  SYSTEM. 

sun^in  an  elliptical  orbit;  then,  accompanying  these, 
the  satellites,  each  revolving  about  its  own  planet, 
while  all  whirl  in  a  dizzy  waltz  about  the  central 
orb ;  next,  the  comets,  rushing  across  the  planetary 
orbits  at  irregular  intervals  of  time  and  space ;  and 
finally,  shooting-stars  and  meteors  darting  hither 
and  thither,  interweaving  all  in  apparently  inextri- 
cable confusion.  To  make  the  picture  more  wonder- 
ful still,  every  member  is  flying  with  an  inconceiv- 
able velocity,  and  yet  with  such  accuracy  that  the 
solar  system  is  the  most  perfect  timepiece  known. 


THE  SUN. 

Sign,  ©,  a  buckler  with  its  boss. 

DISTANCE. — The  sun's  average  distance  from  the 
earth  is  about  ^1^  million  miles.  Since  the  orbit  of 
the  earth  is  elliptical,  and  the  sun  is  situated  at  one 
of  its  foci,  the  earth  is  nearly  3,000,000  miles  further 
from  the  sun  in  aphelion  than  in  perihelion.  As  we 
attempt  to  locate  the  heavenly  bodies  in  space,  we 
are  immediately  startled  by  the  enormous  figures 
employed.  The  first  number,  91,500,000  miles,  is 
far  beyond  our  grasp.  Let  us  try  to  comprehend  it. 
If  there  were  air  to  convey  a  sound  from  the  sun  to 
the  earth,  and  a  noise  could  be  made  loud  enough  to 
pass  that  distance,  it  would  require  over  fourteen 
years  for  it  to  come  to  us.  Suppose  a  railroad 


THE  SUN.  47 

could  be  built  to  the  sun.  An  express-train,  travel* 
ling  day  and  night,  at  the  rate  of  thirty  miles  an 
hour,  would  require  341  years  to  reach  its  desti- 
nation. Ten  generations  would  be  born  and  would 
die  ;  the  young  men  would  become  gray-haired,  and 
their  great-grandchildren  v  ould  forget  the  story  of 
the  beginning  of  that  wonderful  journey,  and  could 
find  it  only  in  history,  as  we  now  read  of  Queen 
Elizabeth  or  of  Shakspeare  ;  the  eleventh  generation 
would  see  the  solar  depot  at  the  end  of  the  route. 
Yet  this  enormous  distance  of  91,500,000  miles  is 
used  as  the  unit  for  expressing  celestial  distances 
— as  the  foot-rule  fop  measuring  space ;  and  astron- 
omers speak  of  so  many  times  the  sun's  distance 
as  we  speak  of  so  many  feet  or  inches. 

The  LIGHT  OP  THE  SUN. — This  is  equal  to  5,563 
wax-candles  held  at  a  distance  of  one  foot  from  the 
eye.  It  would  require  800,000  full-moons  to  pro- 
duce a  day  as  brilliant~as  one  of  cloudless  sunshine. 

THE  HEAT  OF  THE  SUN. — The  amount  of  heat  we 
receive  annually  is  sufficient  to  melt  a  layer  of  ice 
thirty-eight  yards  in  thickness,  extending  over  the 
whole  earth.  Yet  the'  sunbeam  is  only  -sTroVinr  part 
as  intense  as  it  is  at  the  surface  of  the  sun.  More- 
over, the  heat  and  light  stream  off  into  space  equally 
in  every  direction.  Of  this  vast  flood  only  one 
twenty-three  hundred  millionth  part  reaches  the 
earth.  It  is  said  that  if  the  heat  of  the  sun  were 
produced  by  the  burning  of  coal,  it  would  require  a 
layer  ten  feet  in  thickness,  extending  over  the  whole 


48  THE  SOLAR  SYSTEM. 

sun,  to  feed  the  flame  a  single  hour.  Were  the  sun 
a  solid  body  of  coal,  it  would  burn  up  at  this  rate  in 
forty-six  centuries.  Sir  John  Herschel  says  that  if 
a  solid  cylinder  of  ice  45  miles  in  diameter  and 
200,000  miles  long  were  plunged,  end  first,  into  the 
sun,  it  would  melt  in  a  second  of  time. 

APPARENT  SIZE. — It  appears  to  be  about  a  half  de- 
gree in  diameter,  so  that  360  disks  like  the  sun,  laid 
side  by  side,  would  make  a  half  circle  of  the  celestial 
sphere.  It  seems  a  little  larger  to  us  in  winter  than 
in  summer,  as  we  are  3,000,000  miles  nearer  it.  If 
we  represent  the  luminous  surface  of  the  sun  when 
at  its  average  (mean)  distance  by  1000,  the  same  sur- 
face will  be  represented  to  us  when  in  aphelion  (July) 
by  940,  and  when  in  perihelion  (January)  by  1072. 

DIMENSIONS. — Its  diameter  is  about  850,000  miles.* 
Let  us  try  to  understand  this  amount  by  comparison. 

A  mountain  upon  the  surface  of  the  sun,  to  bear 
the  same  proportion  to  the  globe  itself  as  the  Dha- 
walaghiri  of  the  Himalayas  does  to  the  earth,  would 
have  to  be  about  six  hundred  miles  high. 

Again:  Suppose  the  sun  were  hollow,  and  the 
earth,  as  in  the  cut  (Fig.  4),  placed  at  the  centre,  not 
only  would  there  be  room  for  the  moon  to  revolve 
in  its  regular  orbit  within  the  shell,  but  that  would 
stretch  off  in  every  direction  200,000  miles  beyond. 

Its  volume  is  1,245,000  times  that  of  the  earth — 

*  Pythagoras,  whose  theory  of  the  universe  was  in  so  many 
respects  very  like  the  one  we  receive,  believed  the  sun  to  be 
44,000  miles  from  the  earth,  and  75  miles  in  diameter. 


THE  SUN.  49 

t.  e.,  it  would  take  1,245,000  earths  to  make  a  globe 
the  size  of  the  sun.  Its  mass  is  674  times  that  of 
all  the  rest  of  the  solar  system.  Its  weight  may  be 
expressed  in  tons  thus, 

1 , 910 , 278 , 070 , 000 , 000 , 000 , 000 , 000 , 000, 

Fig.  4. 


a  number  which  is  meaningless  to  our  imagination, 
but  yet  represents  a  force  of  attraction  which  holds 
our  own  earth  and  all  the  planets  steadily  in  their 
places ;  while  it  fills  the  mind  with  an  indescribable 
awe  as  we  think  of  that  Being  who  made  the  sun, 
and  holds  it  in  the  very  palm  of  his  hand. 


50  THE  SOLAR  SYSTEM. 

The  density  of  the  sun  is  only  about  one-fourth 
that  of  the  earth,  or  1.43  that  of  water,  so  that 
the  weight  of  a  body  transferred  from  the  earth  to 
the  sun  would  not  be  increased  in  proportion  to  the 
comparative  size  of  the  two.  On  account  also  of 
the  vast  size  of  the  sun,  its  surface  is  so  far  from 
its  centre  that  the  attraction  is  largely  diminished, 
since  that  decreases,  we  remember,  as  the  square  of 
the  distance.  However,  a  man  weighing  at  the 
earth's  equator  150  Ibs.,  at  the  sun's  equator  would 
weigh  about  4,080  Ibs., — a  force  of  attraction  that 
would  inevitably  and  instantly  crush  him.  At  the 
earth's  equator  a  stone  falls  16  feet  the  first  second ; 
at  the  sun's  equator  it  would  fall  437  feet. 

TELESCOPIC  APPEARANCE  OF  THE  SUN  :  SUN-SPOTS.— 
We  may  sometimes  examine  the  sun  at  early  morning 
or  late  in  the  afternoon  with  the  naked  eye,  and  at  mid- 
day by  using  a  smoked  glass.  The  disk  will  appear 
to  us  perfectly  distinct  and  circular,  and  with  no 
spot  to  dim  its  brightness.  If  we  use,  however,  a 
telescope  of  moderate  power,  taking  the  precaution 
to  properly  shield  the  eye  with  a  colored  eye-piece, 
we  shall  find  its  surf  ace  sprinkled  with  irregular  spots, 
somewhat  as  shown  in  the  accompanying  figure. 

Curious  opinions  concerning  solar  spots. — The  nat- 
ural purity  of  the  sun  seems  to  have  been  formerly 
an  article  of  faith  among  astronomers,  and  therefore 
on  no  account  to  be  called  in  question.  Scheiner, 
it  is  said,  having  reported  to  his  superior  that  he 
had  seen  spots  on  the  sun's  face,  was  abruptly  dis- 


THE   SUN. 


51 


missed  with  these  remarks  :  "  I  have  read  Aristotle's 
writings  from  end  to  end  many  times,  and  I  assure 
you  I  do  not  find  anything  in  them  similar  to  that 
which  you  mention.  Go,  my  son,  tranquillize  your- 
self;  be  assured  that  what  you  take  for  spots  are 
the  faults  of  your  glasses  or  your  own  eyes." 


SUN   IN   TELESCOPE. 


Discovery  of  the  solar  spots. — They  seem  to  have 
been  noticed  as  early  as  807  A.  D.,  although  the  tel- 
escope was  not  invented  until  1610,  and  Galileo  dis- 
covered the  solar  spots  in  the  following  year.  We 


52  THE  SOLAR  SYSTEM. 

read  in  the  log-book  of  the  good  ship  Bichard  of 
Arundell,  on  a  voyage,  in  1590,  to  the  coast  of 
Guinea,  that  "  on  the  7,  at  the  going  downe  of  the 
sunne,  we  saw  a  great  black  spot  in  the  sunne ;  and 
the  8  day,  both  at  rising  and  setting,  we  saw  the 
like, — which  spot  to  me  seeming  was  about  the  big- 
nesse  of  a  shilling,  being  in  5  degrees  of  latitude, 
and  still  there  came  a  great  billow  out  of  the  souther 
board." 

Number  and  location  of  spots.  —  Sometimes,  but 
rarely,  the  disk  is  clear.  During  a  period  of  ten 
years,  observations  were  made  on  1982  days,  on  372 
of  which  there  were  no  spots  seen.  As  many  as 
two  hundred  spots  have  been  noticed  at  one  time. 
They  are  found  in  two  belts,  one  on  each  side  of 
the  equator,  within  not  less  than  8°  nor  more  than 
35°  of  latitude.  They  seem  to  herd  together — the 
length  of  the  straggling  group  being  generally  par- 
allel to  the  equator. 

The  size  of  the  spots. — It  is  not  uncommon  to  find 
a  spot  with  a  surface  larger  than  that  of  the  earth. 
Schroter  measured  one  more  than  29,000  miles  in 
diameter.  Sir  J.  W.  Herschel  calculated  that  one 
which  he  saw  was  50,000  miles  in  diameter.  In 
1843  one  was  seen  which  was  14,816  miles  across, 
and  was  visible  to  the  naked  eye  for  an  entire 
week.  On  the  day  of  the  eclipse  in  1858,  a  spot 
over  107,000  miles  broad  was  distinctly  seen,  and 
attracted  general  attention  in  this  country.  Some 
who  read  this  paragraph  will  doubtless  recall  its  ap- 


THE  SUN. 


53 


Fig.  6. 


pearance.  In  1839,  Captain  Davis  saw  one  which 
he  computed  was  not  less  than  186,000  miles  long, 
and  had  an  area  of  twenty-five  billion  square  miles. 
If  these  are  deep  openings  in  the  luminous  atmos- 
phere of  the  sun,  what  an  abyss  must  that  be  at 
"the  bottom  of  which  our  earth  could  lie  like  a 
boulder  in  the  crater  of  a  volcano  !" 

The  spots  consist  of  distinct  part*. — From  the  ac- 
companying representation  it  will  be  seen  that  the 
spots  generally  consist  of  one  or  more  dark  portions 
called  the  umbra,  and  around  that  a  grayish  portion 
styled  the  pe- 
numbra (pene, 
almost,  and  um- 
bra, black). — 
Sometimes,  how- 
ever, umbrae  ap- 
pear without  a 
penumbra,  and 
vice  versa.  The 
umbra  itself  has 
generally  a 
dense  black 
centre,  called  the 
nucleus.  Besides 
this,  the  umbra  is  sometimes  divided  by  luminous 
bridges. 

The  spots  are  in  motion. — They  change  from  day 
to  day;  but  they  all  have  a  common  movement. 
About  fourteen  days  are  required  for  a  spot  to  pass 


SUN  SPOTS. 


54  THE   SOLAR  SYSTEM. 

across  the  disk  of  the  sun  from  the  eastern  side  or 
limb  to  the  western  ;  in  fourteen  days  it  reappears, 
changed  in  form  perhaps,  but  generally  recognizable. 
The  spots  change  their  rapidity  and  apparent  form 
as  they  pass  across  the  dish — A  spot  is  seen  on  the 
eastern  limb  ;  day  by  day  it  progresses,  with  a  grad- 
ually increasing  rapidity,  until  it  reaches  the  cen- 


CHANGE   IN  SPOTS   AS   THEY   CROSS   THE   DISK. 

tre  ;  it  now  gradually  loses  its  rapidity,  and  finally 
disappears  on  the  western  limb.  The  diagram  il- 
lustrates the  apparent  change  which  takes  place  in 
the  form.  Suppose  at  first  it  is  of  an  oval  shape  ; 
as  it  approaches  the  centre  it  apparently  widens 
and  becomes  circular.  Having  passed  that  point, 
it  becomes  more  and  more  oval  until  it  disappears. 

This  change  in  the  spots  proves  the  sun's  rotation 
on  its  axis. — These  changes  can  be  accounted  for 
only  on  the  supposition  that  the  sun  revolves  on  its 
axis  :  indeed,  they  are  the  precise  effects  which  the 


THE  SUN. 


55 


laws  of  perspective  demand  in  that  case.  About 
twenty-seven  days  (27  d.,  7  h.)  elapse  from  the  ap- 
pearance of  a  spot  on  the  eastern  limb  before  it 
reappears  a  second  time.  During  this  time  the 
earth  has  gone  forward  in  its  orbit,  so  that  the 
location  of  the  observer  is  changed ;  allowing  for 
this,  the  sun's  time  of  rotation  is  about  twenty- 
five  days  (25  d.,  8  h.,  10  m. :  Langier.) 


SYNODIC  AND  SIDEREAL  BBVOLUTION. 


Synodic  and  sidereal  revolution  of  the  spots. — We 
can  easily  understand  why  we  make  an  allowance 
for  the  motion  of  the  earth  in  its  orbit.  Suppose  a 


56  THE   SOLAR  SYSTEM. 

solar  spot  at  a,  on  a  line  passing  from  the  centre  of 
the  earth  to  the  centre  of  the  sun.  For  the  spot  to 
pass  around  the  sun  and  come  into  that  same  posi- 
tion again,  requires  about  twenty-seven  days.  But 
during  this  time,  the  earth  has  passed  on  from  T  to 
T'.  The  spot  has  not  only  travelled  around  to  a 
again,  but  also  beyond  that  to  a',  or  the  distance 
from  a  to  a'  more  than  an  entire  revolution.  To  do 
this  requires,  as  we  have  said,  about  two  days.  A 
revolution  from  a  around  to  a'  is  called  a  synodic, 
and  one  from  a  around  to  a  again  is  called  a  sidereal 
revolution. 

The    spots    apparently    do    not    always    move    in 
straight  lines. — Sometimes  their  path  curves  toward 


SEPTEMBER. 


Fig.  9. 

the  north,  and  sometimes  toward  the  south,  as  ID 
the  figure.  This  can  be  explained  only  on  the  sup- 
position that  the  sun's  axis  is  inclined  to  the 
ecliptic  (7°  15'). 

The  spots  have  a  motion  of  their  own. — Besides  the 
motion  already  named  as  assigned  to  the  sun's  rota- 
tion, the  spots  seem  to  have  a  motion  of  their  own, 


THE  SUN.  57 

and  this  fact  is  undoubtedly  the  cause  of  the  va- 
riation in  the  estimates  made  of  the  time  of  the 
sun's  revolution  on  its  axis.  A  spot  near  the  equator 

Fig.  10. 


performs  a  synodic  revolution  in  about  twenty-five 
days,  while  one  half  way  to  either  pole  requires 
twenty-eight  days.  One  spot  was  noticed  which 
had  a  motion  three  times  greater  than  that  of  clouds 
driven  along  by  the  most  violent  hurricane.  Again, 
immense  cyclones  occasionally  pass  over  the  surface 
with  fearful  rapidity,  producing  rotation  and  sudden 
changes  in.  the  spots.  At  other  times,  however,  the 
spots  seem  "  to  set  sail  and  move  across  the  disk  of 
the  sun  like  gondolas  over  a  silver  sea." 

The  spots  change  their  real  form. — Spots  break  out 
and  then  disappear  under  the  very  eye  of  the  astron- 
omer. Wollaston  saw  one  that  seemed  to  be  shat- 

3* 


58  THE   SOLAR   SYSTEM. 

tered  like  a  fragment  of  ice  when  it  is  thrown  on  a 
frozen  surface,  breaking  into  pieces,  and  sliding  off 
in  every  direction.  Sometimes  one  divides  itself 
into  several  nuclei,  while  again  several  nuclei  com- 
bine into  one.  Occasionally  a  spot  will  remain  for 
six  or  eight  rotations,  while  often  one  will  last 
only  half  an  hour.  In  one  case,  Sir.  W.  Herschel 
relates  that  when  examining  a  spot  through  his 
telescope,  he  turned  away  for  a  moment,  and  on 
looking  back  it  was  gone. 

The  appearance  of  the  spots  is  periodical. — It  is  a  re- 
markable fact  that  the  numberof  spots  increases  and 
diminishes  through  a  regular  interval  of  about  11.11 
years.  These  variations  seem  also  to  be  connected 
with  periodical  variations  in  the  aurora,  and  magnet- 
ic earth-currents,  which  interfere  with  the  telegraph. 
The  regular  increase  and  diminution  in  the  spots 
was  discovered  by  Schwabe  of  Prussia,  who  watched 
the  sun  so  carefully  that  it  is  said,  "  for  thirty  year« 
the  sun  never  appeared  above  the  horizon  without 
being  confronted  by  his  imperturbable  telescope.' 
Besides  this,  it  has  now  been  found  that  the  activity 
of  the  sun's  spots  goes  through  another  regular 
period  of  about  56  years.  Independently  of  this 
conclusion,  it  has  also  been  discovered  that  the 
aurora  has  a  similar  period  of  56  years. 

The  spots  are  influenced  by  the  planets. — They  ap- 
pear to  be  especially  sensitive  to  the  approach  of 
Venus,  on  account  of  its  nearness,  and  of  Jupiter, 
because  of  its  size.  The  area  of  the  spots  exposed 


THE  SUN.  59 

to  view  from  the  earth  is  uniformly  greatest  when 
Venus  is  on  the  opposite  side  of  the  sun  from  us, 
and  least  when  on  the  same  side.  When  both 
"Venus  and  Jupiter  are  on  the  side  of  the  sun  op- 
posite to  us,  the  spots  are  much  larger  than  when 
Venus  alone  is  in  that  position.  In  part  explana- 
tion of  this  influence  of  the  planets,  we  may  suppose 
that  they,  in  some  manner,  modify  reflection  on  the 
disk  of  the  sun  exposed  to  their  action,  and  thus 
cause  a  condensation  of  gases. 

The  spots  do  not  influence  the  fruitfulness  of  the  sea- 
son.— Sir  W.  Herschel  first  advanced  the  idea  that 
years  of  abundant  spots  would  be  years  also  of  plen- 
tiful harvest.  This  is  not  now  generally  received. 
What  two  years  could  be  more  dissimilar  than  1859 
and  1860  ?  Both  abounded  in  solar  spots,  yet  one 
was  a  fruitful  year  and  the  other  almost  one  of 
famine  in  Europe. 

The  spots  are  cooler  tJian  the  surrounding  surface. — 
It  seems  that  the  breaking  out  of  a  spot  sensibly 
diminishes  the  temperature  of  that  portion  of  the 
sun's  disk.  The  faculae,  on  the  other  hand,  do  not 
increase  the  temperature.  (Secchi.) 

The  spots  are  depressions  below  the  luminous  surface. 
— This  was  thought  probable  before,  but  is  conclu- 
sively proved  by  the  photographs  of  the  sun,  which 
have  been  taken  in  large  numbers  of  late  at  Kew 
Observatory. 

Comparative  brightness  of  spots  and  sun. — If  we 
represent  the  ordinary  brightness  of  the  sun  by 


60 


THE   SOLAE   SYSTEM. 


1,000,  then  that  of  the  penumbra  would  be  469,  and 
that  of  the  nucleus  7.  There  may  be  much  light 
and  heat  radiated  by  a  spot,  which  seems  totally 
black  as  compared  with  the  sun  :  we  remember  that 
when  we  look  through  even  a  Drummond  light  at 
the  sun,  it  appears  as  a  black  spot  on  the  disk  of 
that  luminary. 

Faculce,  tvillow-leaf,  and  mottled  appearance. — Be- 

sides  the  variety  of 
spots  already  de- 
scribed, there  are 
other  curious  ap- 
pearances worthy  of 
note.  Bright  ridges 
or  streaks  appear, 
which  constitute  the 
most  brilliant  por- 
tions of  the  sun. — 
These  are  called  fa- 
culce.  They  vary 
from  barely  discern- 
ible,  softly-gleaming 
tracts  1,000  miles  long,  to  lofty,  piled-up,  mountain- 
ous regions  40,000  miles  long  and  4,000  broad.  Out- 
side of  the  spots,  the  entire  disk  of  the  sun  is  covered 
with  minute  shady  dots,  giving  it  a  mottled  appear- 
ance not  unlike  that  of  the  skin  of  an  orange,  though 
less  coarse.  Under  a  large  telescope  the  surface  seems 
to  be  entirely  made  up  of  luminous  masses,  imperfectly 
separated  by  dark  dots  called  pores.  These  masses  are 


THE   SUN. 


61 


said  by  Mr.  Nasmyth  to  have  a  "willow-leaf"  shape ; 
many  observers  apply  other  descriptive  terms,  such 
as  "  rice  grains,"  "  untidy  circular  masses,"  "  things 
twice  as  long  as  broad,"  "  granules,"  etc.  The  ac- 
companying cut  represents  the  willow-leafed  struc- 
ture of  the  luminous  surface,  and  also  the  "  bridges" 

Pig.  12. 


WILLOW-LBAF. 


spanning  the  solar  spot.  Indeed,  it  is  said  that 
the  spots  themselves  always  have  their  origin  in  a 
"pore"  which  appears  to  slowly  increase  and  as- 
sume the  blackness  of  an  umbra,  after  which  the 
penumbra  begins  to  appear. 
PHYSICAL  CONSTITUTION  OF  THE  SUN.  —  Of  the  consti- 


62  THE  SOLAR  SYSTEM. 

tution  of  the  sun,  and  consequent  cause  of  the 
solar  spots,  very  little  is  definitely  known.  We  shall 
notice  the  various  theories  now  adopted  by  different 
astronomers. 

WILSON'S  THEORY. — This  theory  supposes  that  the 
sun  is  composed  of  a  solid,  dark  globe,  surrounded 
by  three  atmospheres.  The  first,  nearest  the  black 
body  of  the  sun,  is  a  dense,  cloudy  covering,  pos- 
sessing high  reflecting  power.  The  second  is  called 
the  photosphere.  It  consists  of  an  incandescent  gas, 
and  is  the  seat  of  the  light  and  heat  of  the  sun. 
The  third,  or  outer  one,  is  transparent,  very  like  our 
atmosphere.  According  to  this  theory,  the  spots 
are  to  be  explained  in  the  following  manner.  They 
are  simply  openings  in  these  atmospheres  made  by 
powerful  upward  currents.  At  the  bottom  of  these 
chasms  we  see  the  dark  sun  as  a  mtdeus  at  the 
centre,  and  around  this  the  cloudy  atmosphere — the 
penumbra.  This  explains  a  black  spot  with  its 
penumbra.  Sometimes  the  opening  in  the  photo- 
sphere may  be  smaller  than  that  in  the  inner  or 
cloudy  atmosphere;  in  that  case  there  will  be  a 
black  spot  without  a  penumbra.  It  will  be  natural 
to  suppose  that  when  the  heated  gas  of  the  photo- 
sphere or  second  atmosphere  is  thus  violently  rent 
asunder  by  an  eruption  or  current  from  below, 
luminous  ridges  will  be  formed  on  every  side  of 
the  opening  by  the  heaped-up  gas.  This  will  ac- 
count for  the  faculce  surrounding  the  sun-spots. 
It  will  be  natural,  also,  to  suppose  that  sometimes 


THE   SUN.  63 

the  cloudy  atmosphere  below  will  close  up  first  over 
the  dark  surface  of  the  sun,  leaving  only  an  open- 
ing through  the  photosphere,  disclosing  at  the  bot- 
tom a  grayish  surface  of  penumbra.  We  can  readily 


Fig.  13. 


WILSON  S   THEORY. 


see,  also,  how,  as  the  sun  revolving  on  its  axis  brings 
a  spot  nearer  and  nearer  to  the  centre,  thus  giving  us 
a  more  direct  view  of  the  opening,  we  can  see 
more  and  more  of  the  dark  body.  Then  as  it  passes 
by  the  centre  the  nucleus  will  disappear,  until 
finally  we  can  see  only  the  side  of  the  fissure,  the 


64  THE  SOLAR  SYSTEM. 

penumbra,  which,  in  its  turn,  will  pass  from  our 
sight.  The  existence  of  an  outer  atmosphere  will 
account  for  the  fact  that  the  sun's  margin  is  not  so 
bright  as  its  centre. 

EJRCHHOFF'S  THEORY. — This  view  differs  essentially 
from  that  of  Wilson.  It  considers  the  sun  as  an 
intensely  white-hot  solid  or  fluid  body  surrounded 
by  a  dense  atmosphere  of  flame,  filled  with  sub- 
stances volatilized  by  the  vivid  heat.  Changes  of 
temperature  take  place,  which  give  rise  to  tornadoes 
and  violent  tempests.  Descending  currents  pro- 
duce openings  filled  with  clouds,  which  appear  as 
black  spots  on  the  sun's  disk.  A  cloud  once  formed 
becomes  a  screen  to  shield  the  upper  regions  from 
the  direct  heat  of  the  body  of  the  sun.  Thus  a 
lighter  cloud  is  produced,  which  gives  the  appear- 
ance of  a  penumbra  around  the  spots. 

Spectrum  analysis. — The  hypothesis  just  given  of 
the  constitution  of  the  sun  rests  upon  the  discov- 
eries of  the  spectroscope.  This  subject  will  be 
treated  hereafter  under  the  head  of  Celestial  Chem- 
istry. Wilson's  theory  is  time-honored,  but  compli- 
cated ;  Kirchhoff's  is  modern,  and  partakes  of  the 
simplicity  of  true  science. 

THE  HEAT  OF  THE  SUN. — This  subject  is  not  under- 
stood. Many  theories  have  been  advanced,  but 
none  has.  been  generally  adopted.  Some  have 
supposed  the  heat  is  produced  by  condensation, 
whereby  the  size  of  the  sun  is  being  constantly  de- 
creased. The  dynamic  theory  accounts  for  the  heat 


THE   PLANETS.  65 

and  the  solar  spots  by  assuming  that  there  are  vast 
numbers  of  meteors  revolving  around  the  sun,  and 
that  these  constantly  rain  down  upon  the  surface  of 
that  luminary.  Their  motion  being  stopped  and 
changed  to  heat,  feeds  this  great  central  fire.  Were 
Mercury  to  strike  the  sun  in  this  way,  it  would 
generate  sufficient  heat  to  compensate  the  loss  by 
radiation  for  seven  years.  Many  suppose  that  the 
heat  of  the  sun  is  gradually  diminishing.  Of  this 
we  may  be  assured,  there  is  enough  to  support  life 
on  our  globe  for  millions  of  years  yet  to  come. 


THE  PLANETS. 

WE  shall  describe  these  in  regular  order,  passing 
outward  from  the  sun.  In  this  journey  we  shall  ex- 
amine each  planet  in  turn,  noticing  its  distance, 
size,  length  of  its  year,  duration  of  day  and  night, 
temperature  of  the  climate,  the  number  of  its  moons, 
and  many  other  interesting  facts,  showing  how  much 
we  can  Tmow  of  its  world-life  in  spite  of  its  wonder- 
ful distance.  We  shall  encounter  the  earth  in  our 
imaginary  wanderings  through  space,  and  shall  ex- 
plain many  celestial  phenomena  already  partially 
familiar  to  us.  In  all  these  worlds  we  shall  find 
traces  of  the  same  Divine  hand,  moulding  and 
directing  in  conformity  to  one  universal  plan.  The 
laws  of  light  and  heat  will  be  invariable.  The  law 


66  THE  SOLAR  SYSTEM. 

of  gravitation,  which  causes  a  stone  to  fall  to  the 
ground,  will  be  found  to  apply  equally  to  the-  most 
distant  planets.  Even  the  very  elements  of  which 
they  are  composed  will  be  familiar  to  us,  so  that  a 
book  of  natural  science  published  here  would,  in  all 
its  general  features,  answer  for  use  in  a  school  on 
Mars  or  Jupiter. 

CHARACTERISTICS  COMMON  TO  THE  PLANETS.  (Hind.) 
— 1.  They  move  in  the  same  invariable  direction 
around  the  sun ;  their  course,  as  viewed  from  the 
north  side  of  the  ecliptic,  being  contrary  to  the 
motion  of  the  hands  of  a  watch. 

2.  They  describe  oval  or  elliptical  paths  round 
the  sun — not,  however,  differing  greatly  from  circles. 

3.  Their  orbits  are  more  or  less  inclined  to  the 
ecliptic,  and  intersect  it  in  two  points,  which  are  the 
nodes — one  half  of  the  orbit  lying  north  and  the 
other  south  of  the  earth's  path. 

4.  They  are   opaque  bodies  like  the  earth,  and 
shine  by  reflecting  the  light  they  receive  from  the 
sun. 

5.  They  revolve  upon  their  axes  in  the  same  way 
as  the  earth.     This  we  know  by  telescopic  observa- 
tion to  be  the  case  with  many  planets,  and  by  anal- 
ogy the  rule  may  be  extended  to  all.     Hence  they 
will  have  the  alternation  of  day  and  night  like  the 
inhabitants  of  the  earth  ;  but  their  days  are  of  dif- 
ferent lengths  from  our  own. 

6.  Agreeably  to  the  principles  of  gravitation,  their 
velocity  is  greatest  at  those  parts  of  their  orbit 


THE   PLANETS.  67 

which  are  nearest  the  sun,  and  least  at  the  parts 
which  are  most  distant  from  it ;  in  other  words, 
they  move  quickest  in  perihelion,  and  slowest  in 
aphelion. 

COMPARISON  OF  THE  TWO  GROUPS  OF  THE  MAJOR 
PLANETS.  (Chambers.} — Separating  the  major  plan- 
ets into  two  groups,  if  we  take  Mercury,  Venus,  the 
Earth,  and  Mars  as  belonging  to  the  interior,  and 
Jupiter,  Saturn,  Uranus,  and  Neptune  to  the  exterior 
group,  we  shall  find  that  they  differ  in  the  following 
respects  : 

1.  The  interior  planets,  with  the  exception  of  the 
earth,  are  not,  so  far  as  we  know,  attended  by  any 
satellite,  while  the  exterior  planets  all  have  satel- 
lites.    We  can  but   consider   this   as   one   of  the 
many  instances  to  be  met  with,  in  the  universe,  of 
the  beneficence  of  the  Creator,  and  that  the  satel- 
lites of  these  remote  planets  are  designed  to  com- 
pensate for  the  small  amount  of  light  their  primaries 
receive  from  the  sun,  owing  to  their  great  distance 
from  that  luminary. 

2.  The  average  density  of  the  first  group  consid- 
erably exceeds  that  of  the  second,  the  approximate 
ratio  being  5  : 1. 

3.  The  mean  duration  of  the  axial  rotations,  or 
mean  length  of  the  day  of  the  interior  planets,  is 
much  longer  than  that  of  the  exterior  ;  the  average 
in  the  former  case  being  about  twenty-four  hours, 
but  in  the  latter  only  about  ten  hours. 

THE  PROPERTIES  OF  THE  ELLIPSE. — In  the  figure,  S 


68 


THE  SOLAK  SYSTEM. 


and  S'  are  the  foci  of  the  ellipse  ;  AC  is  the  major 
axis  ;  BD,  the  minor  or  conjugate  axis  ;  O,  the  centre  : 
or,  astronomically,  OA  is  the  semi-axis-major  or  mean 
distance,  OB  the  semi-axis-minor:  the  ratio  of  OS 
to  OA  is  the  eccentricity  ;  the  least  distance,  SA,  is 
the  perihelion  distance  /  the  greatest  distance,  SO, 
the  aphelion  distance. 

Fig.  14. 


CHARACTERISTICS  OF  PLANETARY  ORBIT. — It  will  not 
be  difficult  to  follow  in  the  mind  the  additional 

Fig.  15. 


PLANETABT  ORBITS. 


characteristics  of  a  planet's  orbit.     The   orbit  or 
ellipse  just  given  is  laid  on  a  plane  surface.    Now, 


THE  PLANETS.  69 

incline  it  slightly,  as  compared  with  some  other 
fixed  plane  ring,  as  in  the  cut.  The  astronomical 
fixed  plane  is  the  ecliptic.  Imagine  a  planet  follow- 
ing the  inclined  ellipse  ;  at  some  point  it  must  rise 
above  the  level  of  the  fixed  plane  :  this  point  is 
called  the  ascending  node,  and  the  opposite  point  of 
intersection  is  termed  the  descending  node.  A  line 
connecting  the  two  nodes  is  called  the  line  of  the 
nodes.  The  longitude  of  the  node  is  its  distance  from 
the  first  point  of  Aries,  measured  on  the  ecliptic, 
eastward.  In  this  way  we  can  get  a  very  correct 
idea  of  a  planetary  orbit  in  space. 

COMPARATIVE  SIZE  OF  PLANETS.  (Chambers.) — The 
following  scheme  will  assist  in  obtaining  a  correct 
notion  of  the  magnitude  of  the  planetary  system. 
Choose  a  level  field  or  common  ;  on  it  place  a  globe 
two  feet  in  diameter  for  the  Sun  :  Vulcan  will  then 
be  represented  by  a  small  pin's  head,  at  a  distance 
of  about  27  feet  from  the  centre  of  the  ideal  sun ; 
Mercury  by  a  mustard-seed,  at  a  distance  of  82 
feet ;  Venus  by  a  pea,  at  a  distance  of  142  feet ;  the 
Earth,  also,  by  a  pea,  at  a  distance  of  215  feet; 
Mars  by  a  small  pepper-corn,  at  a  distance  of  327 
feet;  the  minor  planets  by  grains  of  sand,  at  dis- 
tances varying  from  500  to  600  feet.  If  space  will 
permit,  we  may  place  a  moderate-sized  orange 
nearly  one-quarter  of  a  mile  distant  from  the  start- 
ing point  to  represent  Jupiter  ;  a  small  orange  two- 
fifths  of  a  mile  for  Saturn  ;  a  full-sized  cherry  three- 
quarters  of  a  mile  distant  for  Uranus  ;  and  lastly,  a 


70  THE  SOLAR  SYSTEM. 

pluin  1£  miles  off  for  Neptune,  the  most  distant  planet 
yet  known.  Extending  this  scheme,  we  should  find 
that  the  aphelion  distance  of  Encke's  comet  would 


Pig.  16. 


COMPARATIVE   SIZE    OP    PLANETS. 


be  at  880  feet;  the  aphelion  distance  of  Donati's 
comet  of  1858  at  6  miles  ;  and  the  nearest  fixed  star 
at  7,500  miles. 


THE  PLANETS.  71 

According  to  this  scale,  the  daily  motion  of 
Vulcan  in  its  orbit  would  be  4f  feet ;  of  Mercury,  3 
feet ;  of  Venus,  2  feet ;  of  the  Earth,  1|  feet ;  of 
Mars,  1£  feet ;  of  Jupiter,  10J  inches ;  of  Saturn, 
7J  inches  ;  of  Uranus,  5  inches ;  and  of  Neptune,  4 
inches.  This  illustrates  the  fact  that  the  orbital 
velocity  of  a  planet  decreases  as  its  distance  from 
the  sun  increases. 

CONJUNCTIONS  OF  PLANETS. — The  grouping  together 
of  two  or  more  planets  within  a  limited  area  of  the 
heavens  is  a  rare  event.  The  earliest  record  we 
have  is  the  one  of  Chinese  origin,  already  mentioned 
on  page  16,  wherein  it  is  stated  that  a  conjunction  of 
Mars,  Jupiter,  Saturn,  and  Mercury  occurred  in  the 

Fig.  17. 


VENUS  AND  JUPITER  IN  CONJUNCTION,  JANUARY  30,  1868. 

reign  of  the  Emperor  Chuenhio.    Astronomers  tell  I 
us  that  this  actually  took  place  Feb.  28,  2446  B.  c., 
and  that  they  were  between  10°  and  18°  of  Pisces. 
This  was  before  the  Deluge,  so  that  the  fact  must 


72  THE  SOLAR  SYSTEM. 

have  been  afterward  calculated  and  chronicled  in 
their  records.  In  1859,  Venus  and  Jupiter  came  so 
near  each  other  that  they  appeared  to  the  naked  eye 
as  one  object.  In  1725,  Venus,  Mercury,  Jupiter, 
and  Mars  appeared  in  the  same  field  of  the  telescope, 
ARE  THE  PLANETS  INHABITED? — This  question  is 
one  which  very  naturally  arises,  when  we  think  of 
the  planets  as  worlds  in  so  many  respects  similar 
to  our  own.  We  can  give  no  satisfactory  answer. 
Many  think  that  the  only  object  God  can  possibly 
have  in  making  any  world  is  to  form  an  abode  for 
man.  Our  own  earth  was  evidently  fitted  up,  al- 
though perhaps  not  created,  for  this  express  pur- 
pose. Everywhere  about  us  we  find  proofs  of 
special  forethought  and  adaptation.  Coal  and  oil 
in  the  earth  for  fuel  and  light,  forests  for  timber, 
metals  in  the  mountains  for  machinery,  rivers  for 
navigation,  and  level  plains  for  corn.  Our  own 
bodies,  the  air,  light,  and  heat  are  all  fitted  to  each 
other  with  exquisite  nicety.  When  we  turn  to  the 
planets,  we  do  not  know  but  God  has  other  races  of 
intelligent  beings  who  inhabit  them,  or  even  entirely 
different  ends  to  attain.  Of  this,  however,  we  are 
assured,  that,  if  inhabited,  the  conditions  on  which 
life  is  supported  vary  much  from  those  familiar 
to  us.  We  shall  notice  these  more  especially  as  we 
speak  of  the  different  planets.  We  shall  see  (1)  how 
they  differ  in  light  and  heat,  from  seven  times  our 
usual  temperature  to  less  than  -5-^-5- ;  (2)  in  the  in- 
tensity of  the  force  of  gravity,  from  2 \  times  that  of 


THE  PLANETS.  73 

the  earth  to  less  than  -£$  ;  (3)  in  the  constitution  of 
the  planet  itself,  from  a  density  J  heavier  than  that 
of  the  earth  to  one  nearly  that  of  cork.  The  tem- 
perature sweeps  downward  through  a  scale  of  over 

Fig.  18. 


SIZE  OF  SUN  AS  SEEN  PROM  THB  PLANETS. 

2,000°  in  passing  from  Mercury  to  Uranus.     No  hu- 
man being  could   reside  on  the  former,  while  we 

4 


74  THE  SOLAR  SYSTEM. 

cannot  conceive  of  any  polar  inhabitant  who  could 
endure  the  intense  cold  of  the  latter.  At  the  sun, 
one  of  our  pounds  would  weigh  27  pounds  ;  on  our 
moon  the  pound  weight  would  become  only  about 
2  ounces ;  while  on  Vesta,  one  of  the  planetoids, 
a  man  could  easily  spring  sixty  feet  in  the  air  and 
sustain  no  shock.  Yet  while  we  speak  of  these 
peculiarities,  we  do  not  know  what  modification  of 
the  atmosphere  or  physical  features  may  exist  even 
on  Mercury  to  temper  the  heat,  or  on  Uranus  to 
reduce  the  cold.  With,  however,  all  these  diversi- 
ties, we  must  admit  the  power  of  an  all-wise 
Creator  to  create  beings  adapted  to  the  life  and 
the  land,  however  different  from  our  own.  The 
Power  that  prepared  a  world  for  us,  could  as  easily 
and  perfectly  prepare  one  for  other  races.  May 
it  not  be  that  the  same  love  of  diversity,  which  will 
not  make  two  leaves  after  the  same  pattern  nor  two 
pebbles  of  the  same  size,  delights  in  worlds  peopled 
by  races  as  diverse  ?  While,  then,  we  cannot  affirm 
that  the  planets  are  inhabited,  analogy  would  lead 
us  to  think  that  they  are,  and  that  the  most 
distant  star  that  shines  in  the  arch  of  heaven  is 
filled  with  living  beings  under  the  care  and  govern- 
ment of  Him  who  enlivens  the  densest  forest 
with  the  hum  of  insects,  and  populates  even  a 
drop  of  water  with  its  teeming  millions  of  animal- 
eulso. 

DmsiOKS  OF  THE  PLANETS. — The  planets  are  di- 
vided into  two  classes  :  (1)  Inferior,  or  those  whose 


THE  PLANETS.  75 

orbits  are  within  that  of  the  earth — viz.,  Mercury, 
Venus ;  (2)  Superior,  or  those  whose  orbits  are  be- 
yond that  of  the  earth — Mars,  Jupiter,  Saturn, 
Uranus,  Neptune. 

MOTIONS  OF  A  PLANET  AS  SEEN  FROM  THE  SUN. — 
Could  we  stand  at  the  sun  and  watch  the  movements 
of  the  planets,  they  would  all  be  seen  to  be  revolv- 
ing with  different  velocities  in  the  order  of  the 
zodiacal  signs.  But  to  us,  standing  on  one  of  the 
planets,  itself  in  motion,  the  effect  is  changed.  To 
an  observer  at  the  sun  all  the  motions  would  be  real, 
while  to  us  many  are  only  apparent.  The  position 
of  a  planet,  as  seen  from  the  centre  of  the  sun,  is 
called  its  heliocentric  place  ;  as  seen  from  the  centre 
of  the  earth,  its  geocentric  place.  When  Yenus  is  at 
inferior  conjunction,  an  observer  at  the  sun  would 
see  it  in  the  opposite  part  of  the  heavens  from  that 
in  which  it  would  appear  to  him  if  viewed  from  the 
earth. 

MOTIONS  OF  AN  INFERIOR  PLANET. — An  inferior 
planet  is  never  seen  by  us  in  the  part  of  the  sky 
opposite  to  the  sun  at  the  time  of  observation.  It 
cannot  recede  from  him  as  much  as  90°,  or  \  the 
circumference,  since  it  moves  in  an  orbit  entirely 
enclosed  by  the  orbit  of  the  earth.  Twice  in  every 
revolution  it  is  in  conjunction  ( &  )  with  the  sun, — an 
inferior  conjunction  (A)  when  it  comes  between  the 
earth  and  the  sun,  and  a  superior  conjunction  (B) 
when  the  sun  lies  between  it  and  the  earth.  (See 
Fig.  19.) 


76 


THE   SOLAK   SYSTEM. 


When  the  planet  attains  its  greatest  distance  east 
or  west  (as  we  see  it)  from  the  sun,  it  is  said  to  be 
at  its  greatest  elongation,  or  in  quadrature  ( n  ). 


QUADRATURE  AND  CONJUNCTION. 

When  passing  from  B  to  A  it  is  east  of  the  sun,  and 
from  A  to  B  it  is  west  of  the  sun.  When  east  of  the 
sun,  it  sets  later  than  the  sun,  and  hence  is  "  evening 
star  :  "  when  west  of  the  sun,  it  rises  earlier  than  the 
sun,  and  hence  is  "  morning  star."  An  inferior  planet 
is  never  visible  when  in  superior  conjunction,  as  its 
light  is  then  lost  in  the  greater  brilliancy  of  the  sun. 


THE  PLANETS. 


77 


When  in  inferior  conjunction,  it  sometimes  passes  in 
front  of  the  sun,  and  appears  to  us  as  a  round  black 
spot  swiftly  moving  across  his  disk.  This  is  called 
a  transit. 


RETROGRADE  MOTION. 


Retrograde  motion  of  an  inferior  ]danet. — Suppose 
the  earth  to  be  at  A,  and  the  planet  at  B.  Now, 
while  the  earth  is  passing  to  F,  the  planet  will  pass 
to  D — the  arc  AF  being  shorter  than  BD,  because 
the  nearer  a  planet  is  to  the  sun  the  greater  its 
velocity.  While  the  planet  is  at  B,  we  locate  it  a  > 
C  on  the  ecliptic,  in  Gemini ;  but  at  D,  it  appears 
to  us  to  be  at  G,  in  Taurus.  So  that  the  planet  has 
retrograded  through  "an  entire  sign  on  the  ecliptic, 
while  its  course  all  the  while  has  been  directly  for-s 


78  THE  SOLAR  SYSTEM. 

ward  in  the  order  of  the  signs ;  and  to  an  observer  at 
the  sun,  such  would  have  been  its  motion. 

Phases  of  an  inferior  planet — An  inferior  planet 
presents  all  the  phases  of  the  moon.  At  superior 
conjunction,  the  whole  illumined  disk  is  turned  to- 
ward us ;  but  the  planet  is  lost  in  the  sun's  rays : 
therefore  neither  Mercury  nor  Venus  ever  presents  a 
full  circular  appearance,  like  the  full  moon.  A  little 
before  or  after  superior  conjunction,  an  inferior 

Fig.  21. 

>**         JT\ O (V. 

^^O—^—o^-^ 

4)  0  .ft, 

^•^0^ 


PHASES  OF  AN  INFERIOR  PLANET. 


planet  may  be  seen  with  a  telescope  ;  but  the  whole 
of  the  light  side  is  not  turned  toward  us,  and  so  the 
planet  appears  gibbous,  like  the  moon  between  first 
quarter  and  full.  In  quadrature,  the  planet  shows 
us  only  one-half  its  illumined  disk ;  this  decreases, 
becoming  more  and  more  crescent  toward  inferior 
conjunction,  at  which  time  the  unillumined  side  is 
toward  us. 

MOTIONS  OF  A  SUPEKIOB  PLANET. — The  superior 
planet  moves  in  an  orbit  which  entirely  surrounds 


THE  PLANETS.  79 

that  of  the  earth.  When  the  earth  is  at  E  (Fig. 
22),  the  planet  at  L  is  said  to  be  in  opposition  to  the 
sun.  It  is  then  at  its  greatest  distance  from  him — 
180°.  The  planet  is  on  the  meridian  at  midnight 
while  the  sun  is  on  the  corresponding  meridian  on 
the  opposite  side  of  the  earth ;  or  the  planet  may  be 
rising  when  the  sun  is  just  setting.  When  the 
planet  is  at  N,  it  is  in  conjunction,  and  being  lost  in 
the  sun's  rays  is  invisible  to  us. 

Retrograde ' 'motion  of  a  superior  planet. — Suppose 
the  earth  to  be  at  E  and  the  planet  at  L,  and  that 
we  move  on  to  G  while  the  planet  passes  on  to  O — 
the  distance  EG  being  longer  than  LO  (just  the 
reverse  of  what  takes  place  in  the  movements  of 
the  inferior  planets) ;  at  E,  we  should  locate  the 
planet  at  P  on  the  ecliptic,  in  the  sign  Cancer  ;  but 
at  G,  it  would  appear  to  us  at  Q,  in  the  sign  Gemini, 
having  apparently  retrograded  on  the  ecliptic  the 
distance  PQ,  while  it  was  all  the  while  moving  on  in 
the  direct  order  of  the  signs.  Now,  suppose  the 
earth  moves  on  to  I  and  the  planet  to  U,  we  should 
then  see  it  at  the  point  W,  further  on  in  the  ecliptic 
than  Q,  which  indicates  direct  motion  again,  and 
at  some  point  near  Q  the  planet  must  have  appeared 
without  motion.  After  this,  it  will  continue  direct 
until  the  earth  has  completed  a  large  portion  of  her 
orbit,  as  we  shall  easily  see  by  imagining  various 
positions  of  the  earth  and  planet,  and  then  drawing 
lines  as  we  have  just  done,  noticing  whether  they 
indicate  direct  or  retrograde  motion.  The  greater 


80 


THE  SOLAR  SYSTEM. 


the  distance  of  a  planet  the  less  it  will  retrograde, 
as  we  shall  perceive  by  drawing  another  orbit  out- 
side the  one  represented  in  the  cut,  and  making  the 
same  suppositions  concerning  it  as  those  we  have 
already  explained. 


RETROGRADE  MOTION  OF  A  SUPERIOR  PLANET. 

SIDEREAL  AND  SYNODIC  KEVOLUTION. — The  interval 
of  time  required  by  a  planet  to  perform  a  revolution 
from  one  fixed  star  back  to  it  again,  is  termed  a 
sidereal  revolution  (sidus,  a  star). 

1.  The  interval  of  time  between  two  similar  con- 


THE  PLANETS.  81 

junctions  of  an  inferior  planet  with  the  earth  and 
sun  is  termed  a  synodic  revolution.  Were  the  earth 
at  rest,  there  would  be  no  difference  between  a 
sidereal  and  a  synodic  revolution,  and  the  planet 
would  come  into  conjunction  twice  in  each  revolution. 
Since,  however,  the  earth  is  in  motion,  it  follows 
that  after  the  planet  has  completed  its  sidereal 
revolution,  it  must  then  overtake  the  earth  before 
they  can  both  come  again  into  the  same  position 
with  regard  to  the  sun.  The  faster  a  planet  moves, 
the  sooner  it  can  do  this.  Mercury,  travelling  at 
the  greater  speed  and  on  an  inner  orbit,  accom- 
plishes it  much  quicker  than  Yenus.  The  synodic 
period  always  exceeds  the  sidereal. 

2.  The  interval  between  two  successive  conjunc- 
tions or  oppositions  of  a  superior  planet  is  termed  a 
synodic  revolution.  Since  the  earth  moves  so  much 
faster  than  any  superior  planet,  it  follows  that  after 
it  has  completed  a  sidereal  revolution  it  must  then 
overtake  the  planet  before  they  can  come  again  into 
the  same  position  with  regard  to  the  sun.  The 
slower  the  planet  moves,  the  sooner  it  can  do  this. 
Uranus,  making  a  sidereal  revolution  in  eighty-four 
years,  can  be  overtaken  more  quickly  than  Mars, 
which  makes  one  in  less  than  two  years.  It  conse- 
quently requires  over  a  second  revolution  to  catch  up 
with  Mars,  ^  of  one  to  overtake  Jupiter,  and  but 
little  over  y^  of  one  to  come  up  with  Uranus.  In- 
deed, the  earth  repasses  Neptune  in  two  days  after 
it  has  finished  a  sidereal  revolution. 


82  THE  SOLAR  SYSTEM. 

PLANETS  AS  EVENING  AND  MORNING  STARS. — The  in- 
ferior planets  are  evening  stars  from  superior  to 
inferior  conjunction,  and  the  superior  planets  from 
opposition  to  conjunction.  During  the  other  half 
of  their  revolutions  they  are  morning  stars. 

Mercury,  evening  star 2  months. 

Venus,  "          "    9J  '" 

Mars,  "          "    13 

Jupiter,          "          "    6J 

Saturn,  "          "    6 

Uranus,          "          "    6        " 

To  avoid  filling  the  text  with  a  multiplicity  of 
figures,  many  interesting  items  are  condensed  in 
tables  at  the  close  of  the  volume. 

VULCAN. 

SUPPOSED  DISCOVERY. — Le  Verrier,  having  detected 
an  error  in  the  assumed  motion  of  Mercury,  sug- 
gested, in  the  fall  of  1859,  that  there  may  be  an 
interior  planet,  which  is  the  cause  of  this  disturb- 
ance. On  this  being  made  public,  M.  Lescarbault, 
a  French  physician,  and  an  amateur  astronomer, 
stated  that  on  March  26  of  that  year  he  had  seen  a 
dark  body  pass  across  the  sun's  disk,  and  that  this 
might  have  been  the  unknown  planet.  Le  Verrier 
visited  him,  and  found  his  instruments  rough  and 
home-made,  but  singularly  accurate.  His  clock  was 
a  simple  pendulum,  consisting  of  an  ivory  ball  hang- 


MERCURY.  83 

ing  from. a  nail  by  a  silk  thread.  His  observations 
were  on  prescription  paper,  covered  with  grease 
and  laudanum.  His  calculations  were  chalked  on  a 
board,  which  he  planed  off  to  make  room  for  fresh 
ones.  Le  Verrier  became  satisfied  that  a  new  planet 
had  been  really  discovered  by  this  enthusiastic  ob- 
server, and  congratulated  him  upon  his  deserved 
success.  On  March  20,  1862,  Mr.  Lummis,  of  Man- 
chester, England,  noticed  a  rapidly-moving,  dark 
spot,  apparently  the  transit  of  an  inner  planet. 
Many  other  instances  are  given  of  a  somewhat  sim- 
ilar character.  As  yet,  however,  the  existence  of 
the  planet  is  not  generally  conceded.  The  name 
Vulcan  and  the  sign  of  a  hammer  have  been  given 
to  it.  Its  distance  from  the  sun  has  been  estimated 
at  13,000,000  miles,  and  its  periodic  time  (its  year) 
at  20  days. 

MEECUEY. 

The  fleetest  of  the  gods.    Sign,  « ,  his  wand. 

DESCRIPTION. — Mercury  is  nearest  to  the  sun  of 
any  of  the  definitely  known  planets.  ,  When  the  sky 
is  very  clear,  we  may  sometimes  see  it,  just  after 
the  setting  of  the  sun,  as  a  bright  sparkling  star, 
near  the  western  horizon.  Its  elevation  increases 
evening  by  evening,  but  never  exceeds  30°.*  If  we 
watch  it  closely,  we  shall  find  that  it  again  ap- 

*  This  distance  varies  much,  owing  to  the  eccentricity  of  Mcr 
cury's  orbit. 


84  THE  SOLAR  SYSTEM. 

proaclies  the  sun  and  becomes  lost  in  his  rays. 
Some  days  afterward,  just  before  sunrise,  we  can  see 
the  same  star  in  the  east,  rising  higher  each  morn- 
ing, until  its  greatest  elevation  equals  that  which  it 
before  attained  in  the  west.  Thus  the  planet  appears 
to  slowly  but  steadily  oscillate  like  a  pendulum,  to 
and  fro  from  one  side  to  the  other  of  the  sun.  The 
ancients,  deceived  by  this,  failed  to  discover  the  iden- 
tity of  the  two  stars,  and  called  the  morning  star 
Apollo,  the  god  of  day,  and  the  evening  star  Mer- 
cury, the  god  of  thieves,  who  walk  to  and  fro  in  the 
night-time  seeking  plunder.  The  Greeks  gave  to 
Mercury  the  additional  name  of  "The  Sparkling 
One."  The  astrologists  looked  upon  it  as  the  malig- 
nant planet.  The  chemists,  because  of  its  extreme 
swiftness,  applied  the  name  to  quicksilver.  The  most 
ancient  account  that  we  have  of  this  planet  is  given 
by  Ptolemy,  in  his  Almagest ;  he  states  its  location 
on  the  15th  of  November,  265  B.  c.  The  Chinese 
also  state  that  on  June  9,  118  A.  D.,  it  was  near  the 
Beehive,  a  cluster  of  stars  in  Cancer.  Astronomers 
tell  us  that,  according  to  the  best  calculations,  it 
was  at  that  date  within  less  than  1°  of  that  group. 
On  account  of  the  nearness  of  Mercury  to  the  sun, 
it  is  difficult  to  be  detected.*  It  is  said  that  Coper- 
nicus, an  old  man  of  seventy,  lamented  in  his  last 
moments  that,  much  as  he  had  tried,  he  had  never 

*  An  old  English  writer  by  the  name  of  Goad,  in  1686,  humor- 
ously termed  this  planet,  "  A  squinting  lacquey  of  the  sun,  who 
seldom  shows  his  head  in  these  parts,  as  if  he  were  in  debt" 


MERCURY.  85 

been  able  to  see  it.  In  our  latitude  and  climate, 
we  can  generally  easily  detect  it  if  we  watch  for  it 
at  the  time  of  its  greatest  elongation  or  quadrature, 
as  given  in  the  almanac. 

MOTION  IN  SPACE. — It  revolves  about  the  sun  at  a 
mean  distance  of  35,000,000  miles.  Its  orbit  is  the 
most  eccentric  (flattened)  of  any  among  the  eight 
principal  planets,  so  that  although  when  in  peri- 
helion it  approaches  to  within  28,000,000  miles,  in 
aphelion  it  speeds  away  15,000,000  miles  farther,  or 
to  the  distance  of  43,000,000  miles.  Being  so  near 
the  sun,  its  motion  in  its  orbit  is  correspondingly 
rapid — viz.,  30  miles  per  second.  At  this  rate. of 
speed,  we  could  cross  the  Atlantic  Ocean  in  two 
minutes.  The  Mercurial  year  comprises  only  about 
88  days,  or  nearly  three  of  our  months.  Mercury 
revolves  upon  its  axis  in  about  the  same  time  as  the 
earth,  so  that  the  length  of  the  Mercurial  day  is 
nearly  the  same  as  that  of  the  terrestrial  one. 
Though  Mercury  thus  completes  a  sidereal  revolu- 
tion around  the  sun  in  88  days,  yet  to  pass  from  one 
inferior  or  superior  conjunction  to  the  same  again  (a 
synodic  revolution)  requires  116  days.  The  reason 
of  this  is,  as  already  explained,  that  when  Mercury 
comes  around  to  the  same  spot  in  its  orbit  again, 
the  earth  has  gone  forward,  and  it  requires  28  days 
for  the  planet  to  overtake  us. 

DISTANCE  FROM  THE  EARTH. — This  varies  still  more 
than  its  distance  from  the  sun.  At  inferior  conjunc- 
tion it  is  between  the  earth  and  the  sun,  and  its  dis- 


86  THE   SOLAR  SYSTEM. 

tance  from  us  is  the  difference  between  the  distance 
of  the  earth  and  the  planet  from  the  sun  :  at  supe- 
rior conjunction  it  is  the  sum  of  these  distances.  Its 
apparent  diameter  in  these  different  positions  varies 
in  the  same  proportion  as  the  distances,  or  as  three 
to  one.  The  greatest  and  least  distances  vary  ac- 
cording as  either  planet  may  happen  to  be  in  aphe- 
lion or  perihelion.  If  at  inferior  conjunction  Mer- 
cury is  in  aphelion  and  the  earth  in  perihelion,  its 
distance  from  us  is  only  90,000,000  -  43,000,000  = 
47,000,000  miles.  If  at  superior  conjunction  Mer- 
cury is  in  aphelion  and  the  earth  in  aphelion  also, 
its  distance  from  us  is  93,000,000  +  43,000,000  = 
136,000,000  miles. 

DIMENSIONS. — Mercury  is  about  3,000  miles  in  di- 
ameter. Its  volume  is  about  -fa  that  of  the  earth — 
i.  e.,  it  would  require  twenty  globes  as  large  as  Mer- 
cury to  make  one  the  size  of  the  earth,  or  25,000,000 
to  equal  the  sun.  Yet  as  it  is  |  denser  than  the 
earth,  its  weight  is  nearly  ^  that  of  the  earth,  and 
a  stone  let  drop  upon  its  surface  would  fall  7J  feet 
the  first  second.  Its  specific  gravity  is  about  that 
of  tin.  A  pound  weight  removed  to  Mercury  would 
weigh  only  about  seven  ounces. 

SEASONS. — As  Mercury's  axis  is  much  inclined 
from  a  perpendicular,  its  seasons  are  peculiar. 
There  are  no  distinct  frigid  zones;  but  large  re- 
gions near  the  poles  have  six  weeks  continuous  day 
and  torrid  heat,  alternating  with  a  night  of  equal 
length  and  arctic  cold.  The  sun  shines  perpendic- 


MERCUKY. 


87 


ularly  upon  the  torrid  zone  only  at  the  equinoxes, 
while  he  sinks  far  toward  the  southern  horizon  at 
one  solstice,  and  as  far  toward  the  northern  hori- 
zon at  the  other.  The  equatorial  regions,  there- 
fore, modify  their  temperature  during  each  rev- 
Fig.  29 


ORBIT  AND   SEASONS  OF  MERCURY. 


olution  from  torrid  to  temperate,  and  the  tropical 
heat  is  experienced  alternately  toward  the  north 
and  south  of  what  we  call  the  temperate  zones. 
There  is  no  marked  distinction  of  zones  as  with 
us,  but  each  zone  changes  its  character  twice 
during  the  Mercurial  year,  or  eight  times  during 
the  terrestrial  one.  An  inhabitant  of  Mercury 


88  THE  SOLAR  SYSTEM. 

must  be  accustomed  to  the  most  sudden  and  vio- 
lent vicissitudes  of  temperature.  At  one  time  the 
sun  not  only  thus  pours  down  its  vertical  rays,  and  in 
a  few  weeks  after  sinks  far  down  toward  the  horizon, 
but,  on  account  of  Mercury's  elliptical  orbit,  when  in 
perihelion  the  planet  approaches  so  near  the  sun  that 
the  heat  and  light  are  ten  times  as  great  as  that  we 
receive,  while  in  aphelion  it  recedes  so  as  to  reduce 
the  amount  to  four  and  a  half  times  (the  average, 
however,  is  seven  times), — a  temperature  sufficient  to 
turn  water  to  steam,  and  even  to  melt  many  of  the 
metals.  This  entire  round  of  transitions  is  swept 
through  four  times  during  one  terrestrial  year.  The 
relative  length  of  the  days  and  nights  is  much  more 
variable  than  with  us.  The  sun,  apparently  seven 
times  as  large  as  it  seems  to  us,  must  be  a  magnifi- 
cent spectacle,  and  illumine  every  object  with  insuf- 
ferable brilliancy.  The  evening  sky  is,  however, 
lighted  by  no  moon. 

TELESCOPIC  FEATURES. — Under  the  telescope,  Mer- 
cury presents  all  the  phases  of  the  moon,  from  a 
slender  crescent  to  gibbous,  when  its  light  is  lost 
in  that  of  the  sun.  These  phases  prove  that  Mer- 
cury is  spherical,  and  shines  by  the  light  reflected 
from  the  sun.  When  in  quadrature,  it  can  some- 
times be  detected  with  a  telescope  in  daylight. 
Being  an  inferior  planet,  we  can  never  see  it  when 
full,  and  hence  the  brightest,  nor  when  nearest  the 
earth,  as  then  its  dark  side  is  turned  toward  us. 
Owing  to  the  dazzling  light,  and  the  vapors  almost 


VENUS.  89 

always  hanging  around  our  horizon,  this  planet  has 
not  received  much  attention  of  late  ;  the  cuts  here 
given,  and  the  remarks  concerning  its  physical  fea- 
tures, are  based  upon  the  observations  of  the  older 
astronomers.  It  is  thought  by  some  to  have  a 
dense  atmosphere  loaded  with  clouds,  which  would 
materially  diminish  the  intensity  of  the  sun,  and 
perhaps  make  Mercury  quite  habitable.  Sir  W. 
Herschel,  however,  emphatically  denies  this,  and 
asserts  that  the  atmosphere  is  too  insignificant  to 
be  detected.  There  are  some  dark  bands  about  its 
equator.  It  has  lofty  mountains,  which  intercept 
the  light  of  the  sun,  and  deep  valleys  plunged  in 
shade.  One  mountain  has  been  ascertained  to  be 
about  ten  miles  in  height,  which  is  -3^5-  of  the  di- 
ameter of  the  planet.  The  height  of  the  Dhawa- 
laghiri  of  the  Himalayas  is  less  than  29,000  feet, 
or  y^Vir  Par^  of  the  earth's  diameter. 

VENUS. 

The  Queen  of  Beauty.    Sign  ? ,  a  looking-glass. 

DESCRIPTION. — Venus,  the  next  in  order  to  Mer- 
cury, is  the  most  brilliant  of  all  the  planets.  When 
visible  before  sunrise,  she  was  called  by  the  ancients 
Phosphorus,  Lucifer,  or  the  Morning  Star,  and  when 
she  shone  in  the  evening  after  sunset,  Hesperus,  Ves- 
per, or  the  Evening  Star.  She  presents  the  same 
appearances  as  Mercury.  Owing,  however,  to  the 
greater  diameter  of  her  orbit,  her  apparent  oscillations 


90  THE  SOLAB  SYSTEM. 

are  nearly  48°  east  and  west  of  the  sun,*  or  about 
18°  more  than  those  of  Mercury.  She  is  therefore 
seen  much  earlier  in  the  morning  and  much  later  at 
night.  She  is  "  morning  star"  from  inferior  to  supe- 
rior conjunction,  and  "  evening  star"  from  superior 
to  inferior  conjunction.  She  is  the  most  brilliant 
about  five  weeks  before  and  after  inferior  conjunc- 
tion, at  which  time  the  planet  is  bright  enough  to 
cast  a  shadow  at  night.  If,  in  addition,  at  this  time 
of  greatest  brilliancy,  Yenus  is  at  or  near  her  high- 
est north  latitude,  she  may  be  seen  with  the  naked 
eye  in  full  daylight.t  This  occurs  once  in  eight 
years,  in  which  interval  the  earth  and  planet  return 
to  the  same  situation  in  their  orbits ;  eight  complete 
revolutions  of  the  earth  about  the  sun  occupying 
nearly  the  same  time  as  thirteen  of  Venus.  This 
happened  last  in  February,  1862.  A  less  degree 
of  brilliancy  is  attained  once  in  twenty-nine  months, 
under  somewhat  the  same  circumstances. 

MOTION  IN  SPACE. — Unlike  Mercury,  Venus  has 
an  orbit  the  most  circular  of  any  of  the  principal 

*  This  distance  varies  but  little,  owing  to  the  slight  eccentricity 
^>f  Venus's  orbit. 

t  Arago  relates  that  Bonaparte,  upon  repairing  to  the  Luxem- 
bourg, when  the  Directory  was  about  to  give  him  a  fete,  was 
much  surprised  at  seeing  the  multitude  paying  more  attention  to 
the  heavens  above  the  palace  than  to  him  or  his  brilliant  staff. 
Upon  inquiry,  he  learned  that  these  curious  persons  were  observ- 
ing with  astonishment  a  star  which  they  supposed  to  be  that  of 
the  Conqueror  of  Italy.  The  emperor  himself  was  not  indifferent 
when  his  piercing  eye  caught  the  clear  lustre  of  Venus  smiling 
upon  him  at  midday. 


VENUS.  91 

planets.  Her  mean  distance  from  the  sun  is  about 
66,000,000  miles,  which  varies  at  aphelion  and  peri- 
helion within  the  limits  of  a  half  million  miles  against 
15,000,000  miles  in  the  case  of  the  former  planet. 
She  makes  a  complete  revolution  around  the  sun  in 
about  225  da}rs,  at  the  mean  rate  of  22  miles  per 
second ;  hence  her  year  is  equal  to  about  seven  and 
one  half  of  our  months.  This  is  a  sidereal  revolu- 
tion, as  it  would  appear  to  an  observer  at  the  sun, 
but  a  synodic  revolution  is  584  days.  Mercury,  we 
remember,  catches  up  with  the  earth  in  28  days  after 
it  reaches  the  point  where  it  left  the  earth  at  the 
last  inferior  conjunction.  But  it  takes  Venus  nearly 
two  and  a  half  revolutions  to  overtake  the  earth  and 
come  into  the  same  conjunction  again.  This  grows 
out  of  the  fact  that  Yenus  has  a  longer  orbit  to 
travel  through,  and  moves  only  about  one-fifth  faster 
than  the  earth,  while  Mercury  travels  nearly  twice 
as  fast.  The  planet  revolves  upon  its  axis  in  about 
24  hours ;  so  the  day  does  not  differ  in  length  essen- 
tially from  ours. 

DISTANCE  FROM  THE  EARTH. — The  distance  of  Ve- 
nus from  the  earth,  like  that  of  Mercury,  when  in 
inferior  conjunction,  is  the  difference  between  the 
distances*  of  these  two  planets  from  the  sun,  and 
when  in  superior  conjunction  the  sum  of  these  dis- 
tances. 

*  Let  the  pupil  calculate  the  distances  of  the  earth  and  Venus 
from  each  other,  when  in  perihelion  and  aphelion,  as  hi  the  case 
ol  Mercury,  (See  tables  in  Appendix.) 


92 


THE   SOLAR  SYSTEM. 


The  figure  represents  its  apparent  dimensions  at 
the  extreme,  mean,  and  least  distances  from  us. 
The  variation  is  nearly  as  the  numbers  10,  18,  and 
65.  It  would  be  natural  to  think  that  the  planet  is 
the  brightest  when  the  nearest,  and  thus  the  largest, 

Fig.  24. 


EXTREME,  MEAN,  AND  LEAST  APPARENT  SIZE  OP  VENUS. 

but  we  should  remember  that  then  the  bright  side 
is  toward  the  sun,  and  the  unillumined  side  toward 
us.  Indeed,  at  the  period  of  greatest  brilliancy  of 
which  we  have  spoken,  only  about  one-fourth  of 
the  light  is  visible.  At  this  time,  however,  many 
observers  have  noticed  the  entire  contour  of  the 
planet  to  be  of  a  dull  gray  hue,  as  seen  in  the  cut. 

DIMENSIONS. — Venus  is  about  7,500  miles  in  diame- 
ter. The  volume  of  the  planet  is  about  four-fifths 
that  of  the  earth,  while  the  density  is  about  the  same. 
A  stone  let  fall  upon  its  surface  would  fall  14  feet  in 


VENUS.  93 

the  first  second :  a  pound  weight  removed  to  its 
equator  would  weigh  about  five-sixths  of  a  pound. 
From  this  we  see  that  the  force  of  gravity  does  not 
decrease  exactly  in  proportion  to  the  size  of  the 
planet,  any  more  than  it  increases  with  the  mass  of 
the  sun.  The  reason  of  this  is,  that  the  body  is 
brought  nearer  the  mass  of  the  small  planet,  and 
so  feels  its  attraction  more  fully  than  when  far  out 
upon  the  extreme  circumference  of  a  large  body, — 
the  attraction  increasing  as  the  square  of  the  dis- 
tance from  the  particles  decreases. 

SEASONS. — As  the  axis  of  Yenus  is  very  much  in- 
clined from  a  perpendicular,  its  seasons  are  similar 
to  those  of  Mercury.  The  torrid  and  temperate 

Fig.  25 


VENUS  AT  ITS  SOLSTICE. 


zones  overlap  each  other ;  the  polar  regions  having 
alternately  at  one  solstice  a  torrid  temperature,  and 
at  the  other  a  prolonged  arctic  cold.  The  inequality 


94  THE  SOLAR  SYSTEM. 

of  the  nights  is  very  marked.  The  heat  and  light  are 
double  that  of  the  earth,  while  the  circular  form  of 
its  orbit  gives  nearly  an  equal  length  to  its  four 
seasons. 

If  the  inclination  of  its  axis  is  75°,  as  some  as- 
tronomers hold,  its  tropics  must  be  75°  from  the 
equator,  and  its  polar  circles  75°  from  the  poles. 
The  torrid  zone  is,  therefore,  150°  in  width.  The 
torrid  and  frigid  zones  inteiiap  through  a  space  of 
60°,  midway  between  the  equator  and  poles. 

TELESCOPIC  FEATURES. — Venus,  being  an  interior 
planet,  presents,  like  Mercury,  all  the  phases  of  the 
moon.  This  fact  was  discovered  by  Galileo,  and  was 
among  the  first  achievements  of  his  telescopic  obser- 
vations. It  had  been  argued  against  the  Coperni- 
»;an  system  that,  if  true,  Venus  should  wax  and  wane 
Aike  the  moon.  Indeed,  Copernicus  himself  boldly 
declared  that  if  means  of  seeing  the  planets  more 
distinctly  were  ever  invented,  Venus  would  be  found 
to  present  such  phases.  Galileo,  with  his  telescope, 
proved  this  fact,  and,  by  overthrowing  that  objec- 
tion, again  vindicated  the  Copernican  theory.  This 
planet  is  not  sensibly  flattened  at  the  poles.  It  is 
thought  to  have  a  dense,  cloudy  atmosphere.  This 
was  established  by  the  fact  that  at  the  transit  of 
Venus  over  the  sun  in  1761  and  1769,  a  faint  ring 
of  light  was  observed  to  surround  the  black 
disk  of  the  planet.  The  evidence  of  an  atmosphere, 
as  well  as  of  mountains,  rests  very  much  upon  the 
peculiar  appearance  attending  its  crescent  s  ape. 


VENUS. 


95 


(1.)  The  luminous  part  does  not  end  abruptly ;  on 
the  contrary,  its  light  diminishes  gradually,  which 
diminution  may  be  entirely  explained  by  the  twi- 
light on  the  planet.  The  existence  of  an  atmosphere 


Pig.  26. 


CRESCENT  AND   SPOTS   OP  VENU9. 


which  diffuses  the  rays  of  light  into  regions  where 
the  sun  has  already  set,  has  hence  been  inferred. 
Thus,  on  Venus,  the  evenings,  like  ours,  are  lighted 
by  twilight,  and  the  mornings  by  dawn.  (2.)  The 
edge  of  the  enlightened  portion  'of  the  planet  is  un- 
even and  irregular.  This  appearance  is  doubtless 
the  effect  of  shadows  cast  by  mountains.  Spots 
have  been  noticed  on  its  disk  which  are  considered 
to  be  traceable  to  clouds.  Indeed,  Herschel  thinks 
that  we  never  see  the  real  body  of  the  planet,  but 
only  its  atmosphere  loaded  with  vapors,  which  may 
mitigate  the  glare  of  the  intense  sunshine. 

SATELLITES. — Venus  is  not  known  to  have   any 
moon. 


THE  SOLAR  SYSTEM. 


THE  EAUTH. 

Sign,  0,  a  circle  with  Equator  and  Meridian. 

The  Earth  is  the  next  planet  we  meet  in  passing 
outward  from  the  sun.  To  the  beginner,  it  seems 
strange  enough  to  class  our  world  among  the  heav- 
enly bodies.  They  are  brilliant,  while  it  is  dark  and 
opaque  ;  they  appear  light  and  airy,  while  it  is  solid 
and  firm ;  we  see  in  it  no  motion,  while  they  are 
constantly  changing  their  position  ;  they  seem  mere 
points  in  the  sky,  while  it  is  vast  and  extended.  Yet 
at  the  very  beginning  we  are  to  consider  the  earth 
as  a  planet  shining  brightly  in  the  heavens,  and 
appearing  to  other  worlds  as  a  star  does  to  us :  we 
are  to  learn  that  it  is  in  motion,  flying  through  its 
orbit  with  inconceivable  velocity ;  that  it  is  not  fixed, 
but  hanging  in  space,  held  by  an  invisible  power  of 
gravitation  which  it  cannot  evade ;  that  it  is  small 
and  insignificant  beside  the  mighty  globes  that  so 
gently  shine  upon  us  in  the  far-off  sky;  that  our 
earth  is  only  one  atom  in  a  universe  of  worlds,  all 
firm  and  solid,  and  equally  well  fitted  to  be  the  abode 
of  life. 

DIMENSIONS. — The  earth  is  not  "round  like  a  bah1," 
but  flattened  at  the  poles.  Its  form  is  that  of  an 
oblate  spheroid.  Its  polar  diameter  is  about  7,899 
miles,  and  its  equatorial  about  7,925^.  The  com- 
pression is,  therefore,  about  26J  miles.  (See  table 


THE  EARTH. 


97 


in  Appendix.)  If  we  represent  the  earth  by  a  globe 
one  yard  in  diameter,  the  polar  diameter  would  be 
one-tenth  of  an  inch  too  long.  It  has  been  recently 

Fig.  27. 


THE  EARTH  IN  SPACE. 


shown  that  the  equator  itself  is  not  a  perfect  circle, 
but  is  somewhat  flattened,  since  the  diameter  which 


98  THE  SOLAR  SYSTEM. 

pierces  the  meridian  14°  east  of  Greenwich  is  two 
miles  longer  than  the  one  at  right  angles  to  it.  The 
circumference  of  the  earth  is  about  25,000  miles. 
Its  density  is  about  5J  times  that  of  water.  Its 
weight  is 

6,069,000,000,000,000,000,000  tons. 

The  inequalities  of  its  surface,  arising  from  build- 
ings, valleys,  mountains,  etc.,  have  been  likened  to 
the  roughness  on  the  rind  of  an  orange.  This  is 
not  an  exaggeration.  On  a  globe  sixteen  inches  in 
diameter,  the  land,  to  be  in  proportion,  should  be 
represented  by  the  thinnest  writing-paper,  the  hills 
by  small  grains  of  sand,  and  elevated  ranges  by 
thick  drawing-paper.  To  represent  the  deepest 
wells  or  mines,  a  scratch  might  be  made  that  would 
be  invisible  except  with  a  glass.  The  water  in  the 
ocean  could  be  shown  by  a  brush  dipped  in  color 
and  lightly  drawn  over  the  bed  of  the  sea. 

THE  KOTUNDITY  or  THE  EARTH. — This  is  shown  in 
various  ways,  among  which  are  the  following :  (1) 
By  the  fact  that  vessels  have  sailed  around  the  earth  ;* 


*  It  is  curious,  in  connection  with  this  well-known  fact,  lo  re- 
call the  arguments  urged  by  the  Spanish  philosophers  against 
the  reasoning  of  Columbus,  when  he  assured  them  that  he 
could  arrive  at  Asia  just  as  certainly  by  sailing  west  as 
east.  "How,"  they  asked,  "can  the  earth  be  round?  If 
it  were,  then  on  the  opposite  side  the  rain  would  fall  upward, 
trees  would  grow  with  their  branches  down,  and  everything 
would  be  topsy-turvy.  Eveiy  object  on  its  surface  would  cer- 
tainly fall  off;  and  if  a  ship  by  siiVng  west  should  get  around 


THE   EARTH.  9(J 

(2)  when  a  ship  is  coming  into  port  w.e  see  the  masts 
first ;  (3)  the  shadow  of  the  earth  on  the  moon  is 
circular;  (4)  the  polar  star  seems  higher  in  the 
heavens  as  we  pass  north ;  (5)  the  horizon  expands 
as  we  ascend  an  eminence.*  If  we  climb  to  the  top 
of  a  hill,  we  can  see  further  than  when  on  the  plain 
at  its  foot.  Our  eyesight  is  not  improved ;  it  is  only 
because  ordinarily  the  curvature  of  the  earth  shuts 
off  the  view  of  distant  objects,  but  when  we  ascend 
to  a  higher  point,  we  can  see  farther  over  the  side 
of  the  earth.  The  curvature  is  eight  inches  per 
mile,  22  x  8in-  =  32  inches  for  two  miles,  32  x  8in-  for 
three  miles,  etc.  An  object  of  these  respective 
heights  would  be  just  hidden  at  these  distances. 

APPARENT  AND  REAL  MOTION.— In  endeavoring  to 
understand  the  various  appearances  of  the  heavenly 
bodies,  it  is  well  to  remember  how  in  daily  life  we 
transfer  motion.  On  the  cars,  when  in  rapid  move- 
ment, the  fences  and  trees  seem  to  glide  by  us, 

there,  it  would  never  be  able  to  climb  up  the  side  of  the  earth 
and  get  back  again.  How  can  a  ship  sail  up  hill  ?" 

*  The  histoiy  of  aeronautic  adventure  affords  a  curious  illustra- 
tion of  this  same  principle.  The  late  Mr.  Sadler,  the  celebrated 
aeronaut,  ascended  on  one  occasion  in  a  balloon  from  Dublin, 
and  was  wafted  across  the  Irish  Channel,  when,  on  his  approach 
to  the  Welsh  coast,  the  balloon  descended  nearly  to  the  surface 
of  the  sea.  By  this  time  the  sun  was  set,  and  the  shades  of  even- 
ing began  to  close  in.  He  threw  out  nearly  all  his  ballast,  and 
suddenly  sprang  upward  to  a  great  height,  and  by  so  doing 
brought  his  horizon  to  dip  below  the  sun,  producing  the  whole 
phenomenon  of  a  western  sunrise.  Subsequently  descending  in 
Wales,  he,  of  course,  witnessed  a  second  sunset  on  the  same 
evening. 


100  THE  SOLAR  SYSTEM. 

while  we  sit  still  and  watch  them  pass.  On  a 
bridge,  when  we  are  at  rest,  we  follow  the  undula- 
tions of  the  waves,  until  at  last  we  come  to  think 
that  they  are  stationary  and  we  are  sweeping  down 
stream.  "In  the  cabin  of  a  large  vessel  going 
smoothly  before  the  wind  on  still  waterj  or  drawn 
along  a  canal,  not  the  smallest  indication  acquaints 
us  with  the  '  way  it  is  making.'  We  read,  sit, 
walk,  as  if  we  were  on  land.  If  we  throw  a  ball 
into  the  air,  it  falls  back  into  our  hand ;  if  we  drop 
it,  it  alights  at  our  feet.  Insects  buzz  around  us 
as  in  the  free  air,  and  smoke  ascends  in  the  same 
manner  as  it  would  do  in  an  apartment  on  shore. 
If,  indeed,  we  come  on  deck,  the  case  is  in  some 
respects  different ;  the  air,  not  being  carried  along 
with  us,  drifts  away  smoke  and  other  light  bodies 
such  as  feathers  cast  upon  it,  apparently  in  the 
opposite  direction  to  that  of  the  ship's  progress ; 
but  in  reality  they  remain  at  rest,  and  we  leave 
them  behind  in  the  air."* 

DIURNAL  EEVOLUTION  OF  THE  EARTH  AROUND  ITS 
Axis. — The  earth,  in  constantly  turning  from  west 

*  "  And  what  is  the  earth  itself  but  the  good  ship  we  are  sailing 
in  through  the  universe,  bound  round  the  sun ;  and  as  we  sit 
here  in  one  of  the  '  berths,'  we  are  unconscious  of  there  being 
any  'way'  at  all  upon  the  vessel.  On  deck,  too,  out  in  the  open 
air,  it's  all  the  same  as  long  as  we  keep  our  eyes  on  the  ship; 
but  immediately  we  look  over  the  sides — and  the  horizon  is  but 
the  'gunwale'  of  our  vessel — we  see  the  blue  tide  of  the  great 
ocean  around  us  go  drifting  by  the  ship,  and  sparkling  with  its 
million  stars  as  the  waters  of  the  sea  itself  sparkle  at  night  be- 
tween the  tropics  " 


THE  EARTH.  '101 

to  east,  elevates  our  horizon  above  the  stars  on 
the  west,  and  depresses  it  below  the  stars  on  the 
east.  As  the  horizon  appears  to  us  to  be  sta- 
tionary, we  assign  the  motion  to  the  stars,  think- 
ing those  on  the  west  whichjit  «pajsses  6vei>  and 
hides  to  have  sunk  belo^.it  or 
those  on  the  east  it  has. 
moved  above  it  or  risen.  So,  also,  the  horizon  is 
depressed  below  the  sun,  and  we  call  it  sunrise; 
it  is  elevated  above  the  sun,  and  we  call  it  sunset. 
We  thus  see  that  the  diurnal  movement  of  the  sun 
by  day  and  stars  by  night  is  a  mere  optical  delu- 
sion— that  here  as  elsewhere  we  simply  transfer 
motion.  This  seems  easy  enough  for  us  to  under- 
stand, because  the  explanation  makes  it  so  simple  ; 
but  it  was  the  "  stone  of  stumbling"  to  ancient  as- 
tronomers for  two  thousand  years.  Copernicus  him- 
self, it  is  said,  first  thought  of  the  true  solution  while 
riding  on  a  vessel  and  noticing  how  he  insensibly 
transferred  the  movement  of  the  ship  to  the  objects 
on  the  shore.  How  much  grander  the  beautiful 
simplicity  of  this  theory  than  the  cumbersome  com- 
plexity of  the  old  Ptolemaic  belief ! 

Diurnal  motion  of  the  Sun. — The  explanation 
just  given  illustrates  the  apparent  motion  of  the 
sun,  and  the  cause  of  day  and  night.  Suppose  S  to 
be  the  sun.  E,  the  earth,  turning  upon  its  axis 
EF  from  west  to  east,  has  half  its  surface  only  illu- 
minated at  one  time  by  the  sun.  To  a  person  at 
D,  the  sun  is  in  the  horizon  and  day  commences, 


102 


THE   SOLAR  SYSTEM. 


the  luminary  appearing  to  rise  higher  and  higher 
in  the  heavens  with  a  westerly  motion,  as  the  ob- 
server is  carried  forward  easterly  by  the  earth's 
diurnal  rotation  to  A,  where  he  has  the  sun  in  his 


i 

•  •   • 

»0f>.     t     -Vjxrt 


DAILY  MOTION  OP  THE  BUN. 


meridian,  and  it  is  consequently  noon.  The  sun 
then  begins  to  decline  in  the  sky  until  the  specta- 
tor arrives  at  B,  where  it  sets,  or  is  again  in  the 
horizon  on  the  west  side,  and  night  begins.  He 
moves  on  to  C,  which  marks  his  position  at  midnight, 
the  sun  being  then  on  the  meridian  of  places  on 
the  opposite  part  of  the  earth,  and  he  is  then  brought 
round  again  to  D,  the  point  of  sunrise,  when  another 
day  commences.  (Hind.) 

The  unequal  rate  of  diurnal  motion. — Different 
points  upon  .the  surface  of  the  earth  revolve  with 
different  velocities.  At  the  two  poles  the  speed  of 
rotation  is  nothing,  while  at  the  equator  it  is  great- 
est, or  over  1,000  miles  per  hour.  At  Quito,  the 
circle  of  latitude  is  much  longer  than  one  at  the 
mouth  of  the  St.  Lawrence,  and  the  velocities  vary 
in  the  same  proportion.  The  former  place  moves 


THE  EABTH.  103 

at  the  rate  of  about  1,038  miles  per  hour ;  the  lat- 
ter, 450  miles.  In  our  latitude  (41°)  the  speed  is 
about  780  miles  per  hour.  We  do  not  perceive 
this  wonderful  velocity  with  which  we  are  flying 
through  the  air,  because  the  air  moves  with 
us.*  Yet  were  the  earth  suddenly  to  stop  its 
rotation,  the  terrible  shock  would,  without  doubt, 
destroy  the  entire  race  of  man,  and  we,  with  houses, 
trees,  rocks,  and  even  the  oceans,  in  one  confused 
mass,  would  be  hurled  headlong  into  space.  On 
the  other  hand,  were  the  rate  of  rotation  to  increase, 
the  length  of  the  day  would  be  proportionately  short- 
ened, and  the  weight  of  all  bodies  decreased  by  the 
centrifugal  force  thus  produced.  Indeed,  if  the 
rotary  movement  should  become  swift  enough  to 


*  An  ingenious  inventor  once  suggested  that  we  should  utilize 
the  earth's  rotation,  as  the  most  simple  and  economical,  as  well 
as  rapid  mode  of  locomotion  that  could  be  conceived.  This  was 
to  be  accomplished  by  rising  in  a  balloon  to  a  height  inacces- 
sible to  aerial  currents.  The  balloon,  remaining  immovable  in 
this  calm  region,  would  simply  await  the  moment  when  the 
earth,  rotating  underneath,  would  present  the  place  of  destination 
to  the  eyes  of  travellers,  who  would  then  descend.  A  well- 
regulated  watch  and  an  exact  knowledge  of  longitudes  would 
thus  render  travelling  possible  from  east  to  west,  all  voyages 
north  or  south  naturally  being  interdicted.  This  suggestion  has 
only  one  fault ;  it  supposes  that  the  atmospheric  strata  do  not 
revolve  with  the  earth.  Upon  that  hypothesis,  since  we  rotate 
in  our  latitude  with  the  velocity  of  333  yards  hi  a  second,  there 
would  result  a  wind  in  the  contrary  direction  ten  times  more 
violent  than  the  most  terrible  hurricane.  Is  not  the  absence  of 
such  a  state  of  things  a  convincing  proof  of  the  participation  of 
the  atmospheric  envelope  in  the  general  movement  ?  (Guillemin.) 


104 


THE   SOLAR  SYSTEM. 


reduce  the  day  to  84  minutes,  or  about  ^\  its  pres- 
ent length,  the  force  of  gravity  would  be  overcome, 
and,  at  the  equator,  all  bodies  would  be  without 
weight;  if  the  speed  were  still  further  increased, 
loose  bodies  would  fly  off  from  the  earth  like  water 
from  a  grindstone  when  swiftly  turned,  while  we 
should  be  compelled  to  constantly  "hold  on"  to 
avoid  sharing  the  same  fate.  But  against  such  a 
catastrophe  we  are  assured  by  the  immutability  of 
God's  laws.  "  He  is  the  same  yesterday,  to-day, 
and  forever."  The  earth  has  not  varied  in  its  revo- 
lution T£-jj  of  a  second  in  2,000  years. 


Unequal  diurnal  orbits  of  the  stars. — Let  O  repre- 
sent our  position  on  the  earth's  surface,  E  Z  B  our 
meridian ;  E  I B  K  our  horizon  ;  P  and  P'  the  north 


THE  EARTH.  105 

and  south  poles,  Z  the  zenith,  Z'  the  nadir;  and 
GICK  the  celestial  equator.  Now  PB,  it  will  be 
seen,  is  the  elevation  of  the  north  pole  above  the 
horizon,  or  the  latitude  of  the  place.  Suppose  we 
should  see  a  star  at  A,  on  the  meridian  below  the 
pole.  The  earth  revolves  in  the  direction  GIG;  the 
star  will  therefore  move  along  A  L  to  Z,  when  it  is 
on  the  meridian  above  the  pole.  It  continues  its 
course  along  the  dotted  line  around  to  A  again,  when 
it  is  on  the  meridian  below  the  pole,  having  made  a 
complete  circuit  around  the  pole,  but  not  having 
descended  below  our  horizon.  A  star  rising  at  B 
would  just  touch  the  horizon ;  one  at  I  would  move 
on  the  celestial  equator,  and  would  be  above  the 
horizon  as  long  time  as  it  is  below — twelve  hours  in 
each  case ;  a  star  rising  at  M,  would  just  come  above 
the  horizon  and  set  again  at  N. 

Unequal  diurnal  velocities  of  the  stars. — The  stars 
appear  to  us  to  be  set  in  a  concave  shell  which  ro- 
tates daily  about  the  earth.  As  different  parts  of 
the  earth  really  revolve  with  varying  velocities,  so 
the  stars  appear  to  revolve  at  different  rates  of  speed. 
Those  near  the  pole,  having  a  small  orbit,  revolve 
very  slowly,  while  those  near  the  celestial  equator 
move  at  the  greatest  speed. 

Appearance  of  the  stars'  at  different  places  on  the 
earth. — Were  we  placed  at  the  north  pole,  Polaris 
would  be  directly  overhead,  and  the  stars  would 
seem  to  pass  around  us  in  circles  parallel  to  the 
horizon,  and  increasing  in  diameter  from  the  upper 

5* 


106  THE   SOLAR   SYSTEM. 

to  lower  ones.  Were  we  placed  at  the  equator,  the 
pole-star  would  be  at  the  horizon,  and  the  stars 
would  move  in  circles  exactly  perpendicular  to  the 
horizon,  and  decreasing  in  diameter,  north  and  south 
from  those  in  the  zenith,  while  we  could  see  one 
half  of  the  path  of  each  star.  Were  we  placed  in  the 
southern  hemisphere,  the  circumpolar  stars  would 
rotate  about  the  south  pole,  and  the  others  in  cir- 
cles resembling  those  in  our  sky,  only  the  points  of 
direction  would  be  reversed  to  correspond  with  the 
pole.  Were  we  placed  at  the  south  pole,  the  ap- 
pearance would  be  the  same  as  at  the  north  pole, 
except  that  there  is  no  star  to  mark  the  direction  of 
the  earth's  axis. 

MOTION  OF  THE  EARTH  IN  SPACE  ABOUT  THE  SUN. — 
The  earth  revolves  in  an  elliptical  path  about  the 
sun  at  a  mean  distance  of  91  \  million  of  miles.  This 
path  is  called  the  ecliptic  ;  its  eccentricity,  which  is 
greater  than  that  of  the  orbit  of  Venus,  changes 
about  j-oo~f oTo  Per  century,  so  that  in  time  the  orbit 
would  become  circular,  were  it  not  that  after  the 
lapse  of  some  thousands  of  years,  the  eccentricity 
will  begin  to  increase  again,  and  will  thus  vary 
through  all  ages  within  definite,  although  yet  un- 
determined limits.  Its  entire  circumference  is  near- 
ly 600,000,000  miles,  and  the  earth  pursues  this 
wonderful  journey  at  the  rate  of  18  miles  per  second. 
This  revolution  of  the  earth  about  the  sun  gives  rise 
to  various  phenomena,  of  which  we  shall  now  proceed 
to  speak. 


THE  EARTH.  107 

1.  Change  in  the  appearance  of  the  heavens  in  differ- 
ent months. — This  is  the  natural  result  of  the  revolu- 
tion of  the  earth  about  the  sun.  In  Fig.  30,  suppose 


Fig.  30. 


APPEARANCE  OF  THE  HEAVENS  IN  DIFFERENT  SEASONS. 

A  B  C  D  to  be  the  orbit  of  the  earth,  and  E  F  G 
H  the  sphere  of  the  fixed  stars,  surrounding  the 
sun  in  every  direction.  When  our  globe  is  at  A,  the 
stars  about  E  are  on  the  meridian  at  midnight. 
Being  seen  from  the  earth  in  the  opposite  quarter 


108  THE  SOLAR  SYSTEM. 

to  the  sun,  they  are  most  favorably  placed  for  obser- 
vation. The  stars  at  G,  on  the  contrary,  will  be  invisible, 
for  the  sun  intervenes  between  them  and  the  earth : 
they  are  on  the  meridian  of  the  spectator  about  the 
same  time  as  the  sun,  and  are  always  hidden  in  his 
rays.  In  three  months  the  earth  has  passed  over 
one-fourth  of  her  orbit,  and  has  arrived  at  B.  Stars 
about  F  now  appear  on  the  meridian  at  midnight, 
while  those  at  E,  which  previously  occupied  their 
places,  have  descended  toward  the  west  and  are 
becoming  lost  in  the  sun's  refulgence,  while  those 
about  G  are  just  coming  into  sight  in  the  east.  In 
three  months  more  the  earth  is  situated  at  C,  and 
stars  about  G  shine  in  the  midnight  sky,  those  at  F 
having,  in  their  turn,  vanished  in  the  west.  Stars 
at  E  are  on  the  meridian  at  noon,  and  consequently 
hidden  in  daylight ;  and  those  about  H  are  just 
escaping  from  the  sun's  rays,  and  commencing  their 
appearance  in  the  east.  One  revolution  of  the 
earth  brings  the  same  stars  again  on  the  meridian 
at  midnight.  Thus  it  is  that  the  earth's  motion 
round  the  sun  as  a  centre  explains  the  varied  aspect 
of  the  heavens  in  the  summer  and  winter  skies. 
(Hind.) 

2.  Yearly  path  of  the  sun  through  the  heavens. — We 
have  spoken  of  the  diurnal  motion  of  the  sun.  "We 
now  speak  of  its  second  apparent  motion — its  yearly 
path  among  the  stars.*  If  we  look  at  the  accom- 

*  This  yearly  movement  of  the  sun  among  the  fixed  stars  is 
not  as  apparent  to  us  as  his  daily  motion,  because  his  superior 


THE  EARTH.  109 

panying  plate  (Fig.  31),  we  can  see  how  the  motion 
of  the  earth  in  its  orbit  is  also  transferred  to  the 
sun,  and  causes  him  to  appear  to  us  to  travel  in  a 
fixed  path  through  the  heavens.  When  the  earth  is 
in  any  part  of  the  ecliptic,  the  sun  seems  to  us  to  be 
in  the  point  directly  opposite.  For  example,  when 
the  earth  is  in  Libra  (=£=)* — autumnal  equinox — the 
sun  is  in  Aries (T) — vernal  equinox;  when  the  sun 
enters  the  next  sign,  Taurus  («),  the  earth  in  fact 
has  passed  on  to  Scorpio  (^).  Thus  as  the  earth 
moves  through  her  orbit,  the  sun  seems  to  pass 
through  the  same  path  along  the  opposite  side  of  the 
ecliptic,  making  the  entire  circuit  of  the  heavens  in 
the  year,  and  returning  at  the  end  of  that  time  to  the 
same  place  among  the  stars.  If  the  earth  could  leave 
a  shining  line  as  it  passes  through  its  orbit  about  the 
sun,  we  should  see  the  sun  apparently  moving  along 
this  same  line  on  the  opposite  side  of  the  circle. 
We  therefore  define  the  ecliptic  as  the  real  orbit  of 
the  earth  about  the  sun,  or  the  apparent  path  of  the  sun 
through  the  heavens.  The  ecliptic  crosses  the  celes- 
tial equator  at  two  points.  These  are  called  the 


light  blots  out  the  stars.  But  if  we  notice  a  star  at  the  western 
horizon  just  at  sunset,  we  can  tell  what  constellation  the  sun  is 
then  hi :  now  wait  two  or  three  nights,  and  we  shall  find  that  star 
is  set,  and  another  has  taken  its  place.  Thus  we  can  trace  the 
sun  through  the  year  in  his  path  among  the  fixed  stars. 

*  When  we  say  "  the  earth  is  hi  Libra,"  we  mean  that  a  spec- 
tator placed  at  the  sun  would  see  the  earth  hi  that  part  of  the 
heavens  which  is  occupied  by  the  sign  Libra. 


110  THE  SOLAR  SYSTEM. 

3.  An  apparent  movement  of  the  sun,  north  and 
south. — Having  now  spoken  of  the  apparent  diurnal 
and  annual  motions  of  the  sun,  there  yet  remains  a 
third  motion,  which  has  doubtless  oftentimes  at- 
tracted our  attention.     In  summer,  at  midday,  the 
sun  is  high  in  the  heavens  ;  in  the  winter,  quite  low, 
near  the  southern  horizon.     In  summer  he  is  a  long 
time  above  the  horizon ;  in  the  winter,  a  short  time. 
In  summer  he  rises  and  sets  north  of  the  east  and 
west  points ;  in  winter,  south  of  the  east  and  west 
points.     This  subject  is  so  intimately  connected  with 
the  next,  that  we  shall  understand  it  best  when  taken 
in  connection  with  it. 

4.  CHANGE  OF  THE  SEASONS. — VARIATION  IN  LENGTH 
OF  DAY  AND  NIGHT. — By  closely  studying  the  accom- 
panying illustration  and  imagining  the  various  posi- 
tions of  the  earth  in  its  orbit,  let  us  try  to  under- 
stand the  several  points. 

I.  Obliquity  of  the  ecliptic. — The  axis  of  the  earth 
is  inclined  23J°  from  a  perpendicular  to  its  orbit. 
This  angle  is  called  the  obliquity  of  the  ecliptic. 

II.  Parallelism  of  the  axis. — In  all  parts  of    the 
orbit,  the  axis  of  the  earth  is  parallel  to  itself  and 
constantly  points  toward  the  North  Star.*     This  is 
only  an  instance  of  what  is  very  familiar  to  us  all. 
Nature  reveals  to  us  nothing  more  permanent  than 
the  axis  of   rotation  in  anything    that    is  rapidly 
turned.     It  is  its  rotation  which  keeps  a  boy's  hoop 

*  There  is  a  slight  variation  from  this,  which  we  shall  soon 
notice. 


THE   EARTH. 
Fig.  31. 


Ill 


THB  ORBIT  OF  THE   EABTH- 


112  THE  SOLAR  SYSTEM. 

from  falling.  For  the  same  reason  a  quoit  retains 
its  direction  when  whirled,  and  it  will  keep  in  the 
same  plane  at  whatever  angle  it  may  be  thrown. 
A  man  slating  a  roof  wishes  to  throw  a  slate  to  the 
ground ;  he  simply  whirls  it,  and  as  it  descends  it 
will  strike  on  the  edge  without  breaking.  As  long 
as  a  top  spins  there  is  no  danger  of  its  falling, 
since  its  tendency  to  preserve  parallel  its  axis  of 
rotation  is  greater  than  the  attraction  of  the  earth. 
This  wonderful  law  would  lead  us  to  think  that 
the  axis  of  the  earth  always  points  in  the  same 
direction,  even  if  we  did  not  know  it  from  direct 
observation. 

III.  TJie  rays  of  the  sun  strike  the  various  por- 
tions of  the  earth,  when  in  any  position,  at  different 
angles. — Example.     "When  the  earth  is  in  Libra,  and 
also  when  in  Aries,  the  rays  strike  vertically  at  the 
equator,  and  more  and  more  obliquely  in  the  northern 
and  southern  hemispheres,  as  the  distance  from  the 
equator  increases,   until   at  the  poles  they  strike 
almost  horizontally.     This  variation  in  the  direction 
of  the  rays  produces  a  corresponding  variation  in 
the  intensity  of  the  sun's  heat  and  light  at  dif- 
ferent places,  and  accounts  for  the  difference  between 
the  torrid  and  polar  regions. 

IV.  As  the  earth  changes  its  position  the  angle  at 
which  the  rays  strike  any   portion  is  varied. — Ex- 
ample.    Take  the   earth   as  it  enters  Capricornus 
(\s)    and  the  sun  in  Cancer  (©)      He  is  now  over- 
head,  23J°  north  of  the  equator.     His  rays  strike 


THE   EARTH.  113 

less  obliquely  in  tire  northern  hemisphere  than 
when  the  earth  was  in  Libra.  Let  six  months 
elapse :  the  earth  is  now  in  Cancer  and  the  sun  in 
Capricornus;  and  he  is  overhead,  23J°  south  of 
the  equator.  His  rays  strike  less  obliquely  in  the 
southern  hemisphere  than  before,  but  in  the  northern 
hemisphere  more  obliquely.  These  six  months  have 
changed  the  direction  of  the  sun's  rays  on  every 
part  of  the  earth's  surface.  This  accounts  for  the  dif- 
ference in  temperature  between  summer  and  winter. 

V.  The  Equinoxes. — At    the    equinoxes  one  half 
of     each    hemisphere     is   illuminated :   hence  the 
name  Equinox  (cequus,  equal,  and  nox,  night).     At 
these  points  of  the  orbit  the  days  and  nights  are 
equal    over   the  entire  earth,*  each    being   twelve 
hours  in  length. 

VI.  Northern  and  southern  hemispheres  unequally 
illuminated. — While   one  half  of  the   earth  is  con- 
stantly illuminated,  at  all  points  in  the  orbit  except 
the   equinoxes    the  proportion  of  the  northern  or 
southern  hemisphere  which  is  in  daylight  or  dark- 
ness varies.      When    more   than  half  of  a  hemi- 
sphere  is  in  the   light,  its  days   are  longer  than 
the  nights,  and  vice  versa. 

VII.  The  seasons  and    the   comparative  length  of 
days  and  nights  in  the  South  Temperate  Zone,  at  any 
specified  time,  are  the  reverse  of  those  in  the  North 
Temperate  Zone,  except  at  the  Equinoxes,  where   the 
days  and  nights  are  of  equal  length. 

*  Except  a  small  space  at  each  pole. 


114  THE  SOLAB  SYSTEM. 

VIII.  The  earth  at  the  Summer  Solstice. — When 
the   earth  is    at  the   summer   solstice,   about    the 
21st  of  June,  the  sun  is  overhead  23J°  north  of  the 
equator,  and  if  its  vertical  rays  could  leave  a  gold- 
en line  on  the  surface  of  the  earth  as  it  revolves,  they 
would  mark  the  Tropic  of  Cancer.     The  sun  is  at 
its  furthest  northern  declination,  ascends  the  high- 
est it  is  ever  seen  above  our  horizon,  and  rises  and 
sets  23  J°  north  of  the  east  and  west  points.     It  seems 
now  to  stand  still  in  its  northern  and  southern  course, 
and  hence  the  name  Solstice  (sol,  the  sun,  sto,  to 
stand).      The   days    in  the  north  temperate   zone 
are  longer  than  the  nights.     It  is  our  summer,  and 
the  21st  of  June  is  the  longest  day  of  the  year.     In 
the    south    temperate   zone  it  is  winter,   and  the 
shortest  day  of  the  year.      The  circle  that  sepa- 
rates day    from    night    extends  23^°    beyond    the 
north  pole,  and  if  the  sun's  rays  could  in  like  manner 
leave  a  golden  line  on  that  day,  they  would  trace 
on  the  earth  the  Arctic  Circle.    It  is  the  noon  of 
the  long   six    months  polar  day.      The  reverse  is 
true  at    the  Antarctic  Circle,  and    it   is  there  the 
midnight  of  the  long  six  months  polar  night. 

IX.  The  earth  at    the  Autumnal    Equinox. — The 
earth  crosses  the  aphelion  point  the   1st  of  July, 
when  it  is  at  its  furthest   distance  from  the  sun, 
which  is  then  said  to  be  in  apogee.     The  sun  each 
day  rising  and  setting  a  trifle  farther  toward  the 
south,  passes  through  a  lower  circuit  in  the  heavens. 
We  reach  the  autumnal  equinox  the  22d  of  Sep- 


THE  EABTH.  115 

tember.  The  sun  being  now  on  the  equinoctial,  if 
its  vertical  rays  could  leave  a  line  of  golden  light, 
they  would  -mark  on  the  earth  the  circle  of  the 
equator.  It  is  autumn  in  the  north  temperate  zone 
'and  spring  in  the  south  temperate  zone.  The  days 
and  nights  are  equal  over  the  whole  earth,  the  sun 
rising  at  6  A.  M.  and  setting  at  6  p.  M.,  exactly  in  the 
east  and  west  where  the  equinoctial  intersects  the 
horizon. 

X.  The  earth  at  the  Winter  Solstice. — The  sun 
after  passing  the  equinoctial — "crossing  the  line," 
as  it  is  called — sinks  lower  toward  the  southern  ho- 
rizon each  day.  We  reach  the  winter  solstice  the 
21st  of  December.  The  sun  is  now  directly  overhead 
23J°  south  of  the  equator,  and  if  its  rays  could 
leave  a  line  of  golden  light  they  would  mark  on 
the  earth's  surface  the  Tropic  of  Capricorn.  It 
is  at  its  furthest  southern  declination,  and  rises  and 
sets  23J°  south  of  the  east  and  west  points.  It 
is  our  winter,  and  the  21st  of  December  is  the  short- 
est day  of  the  year.  In  the  south  temperate 
zone  it  is  summer,  and  the  longest  day  of  the 
year.  The  circle  that  separates  day  from  night 
extends  23J°  beyond  the  south  pole,  and  if  the  sun's 
rays  in  like  manner  could  leave  a  line  of  golden  light 
they  would  mark  the  Antarctic  Circle.  It  is  there 
the  noon  of  the  long  six  months  polar  day.  At 
the  Arctic  Circle  the  reverse  is  true ;  the  rays  fall 
23|°  short  of  the  north  pole,  and  it  is  there  the 
midnight  of  the  long  six  months  polar  night.  Here 


116  THE  SOLAR  SYSTEM. 

again  the  sun  appears  to  us  to  stand  still  a  day 
or  two  before  retracing  its  course,  and  it  is  there- 
fore called  the  Winter  Solstice. 

XI.  The  earth  at  the  Vernal  Equinox. — The  earth 
reaches  its  perihelion  about  the  31st  of  December. 
It  is  then  nearest  the  sun,  which  is  therefore  said 
to  be  in  perigee.     The  sun  rises  and  sets  each  day 
further  and  further  north,  and   climbs  up   higher 
in  the    heavens    at  midday.     Our  days   gradually 
increase  in  length,  and  our  nights  shorten  in  the 
same  proportion.     On  the  21st  of  March*  the  sun 
reaches  the  equinoctial,  at  the  vernal  equinox.     He 
is  overhead  at  the  equator,  and  the  days  and  nights 
are  again  equal.     It  is  our  spring,  but  in  the  south 
temperate  zone  it  is  autumn. 

XII.  The  yearly  path  finished. — The  earth  moves 
on  in  its   orbit  through   the   spring  and  summer 
months.     The   sun  continues  its  northerly  course, 
ascending  each  day  higher  in  the  heavens,  and  its 
rays  becoming  less  and  less  oblique.     On  the  21st 
of  June  it  again  reaches  its  furthest  northern  decli- 
nation, and  the  earth  is  at  the  summer  solstice.   We 
have  thus  traced  the  yearly  path,  and  noticed  the 
course  of  the  changing  seasons,  with  the  length  of 
the  days  and  nights.     The   same  series  has  been 
repeated  through  all  the  ages  of  the  past,  and  will 
be  till  time  shall  be  no  more. 

XIII.  Distance  of  the  earth  from  the  sun  varies. — 

*  The  precise  time  of  the  equinoxes  and  solstices  varies  each 
year,  but  within  a  small  limit. 


THE  EARTH.  117 

We  notice,  from  what  we  have  just  seen,  that  we.  are 
nearer  the  sun  by  3,000,000  miles  in  winter  than  in 
summer.  The  obliqueness  with  which  the  rays 
strike  the  north  temperate  zone  at  that  time  pre- 
vents our  receiving  any  special  benefit  from  this 
favorable  position  of  the  earth. 

XIV.  Southern  summer. — The  inhabitants  of  the 
south  temperate  zone  have  then:  summer  while  the 
earth  is  in  perihelion,  and  the  sun's  rays  are  about 
^warmer  than  when  in  aphelion,  our  summer-time. 
This  will  perhaps  partly  account  for  the  extreme  heat 
of  their  season.     Herschel  tells  us  that  he  has  found 
the  temperature  of  the  surface  soil  of  South  Africa 
159°  F.     Captain  Sturt,  in  speaking  of  the  extreme 
heat  of  Australia,  says  that  matches   accidentally 
dropped  on  the  ground  were  immediately  ignited. 
The    southern   winters,   for   a   similar   reason,   are 
colder ;  and  this  makes  the  average  yearly  tempera- 
ture about  the  same  as  ours. 

XV.  Extremes  of  heat  and  cold  not  at  the  solstices. — 
We  notice  that  we  do  not  have  our  greatest  heat  at 
the  time  of  the  summer  solstice,  nor  our  greatest 
cold  at  the  winter  solstice.     After  the  21st  of  June, 
the   earth,  already  warmed  by  the   genial  spring 
days,  continues  to  receive  more  heat  from  the  sun 
by  day  than  it  radiates  by  night :  thus  its  tempera- 
ture still  increases.     On  the  other  hand,  after  the 
21st   of  December  the  earth  continues  to  become 
colder,  because  it  loses  more  heat  during  the  night 
than  it  receives  during  the  day. 


118  THE  SOLAR  SYSTEM. 

XYI.  Summer  longer  than  winter. — As  the  sun  is 
not  in  the  centre  of  the  earth's  orbit,  but  at  one 
of  its  foci,  that  portion  of  the  orbit  which  the  earth 
passes  through  in  going  from  the  vernal  to  the 
autumnal  equinox  comprises  more  than  one-half  the 
entire  ecliptic.  On  this  account  the  summer  is 
longer  than  the  winter.  The  difference  is  still  fur- 
ther enhanced  by  the  variation  in  the  earth's  ve- 
locity at  aphelion  and  perihelion.  The  annexed 
table  gives  the  mean  duration  of  the  seasons  : 

Seasons.  Days.  Seasons.  Days. 

Spring 92.9        Autumn 89.7 

Summer .93.6        Winter 89.0 

The  difference  of  time  in  the  earth's  stay  in  the 
two  portions  of  the  ecliptic,  as  will  be  seen  from  the 
above,  is  7.8  days. 

XVII.  Varying  velocity  of  the  earth. — We  can  see, 
by  looking  at  the  plate,  that  the  velocity  of  the 
earth  must  vary  in  different  portions   of  its  orbit. 
When  passing  from  the  vernal  equinox  to  aphelion, 
the  attraction  of  the  sun  tends  to  check  its  speed ; 
from  that  point  to  the  autumnal  equinox,  the  at- 
traction is  partly  in  the   direction   of  its  motion, 
and  so  increases  its  velocity.     The  same  principle 
applies  when  going  to  and  from  perihelion. 

XVIII.  Curious  appearance  of  the  sun  at  the  north 
pole. — "  To  a  person  standing  at  the  north  pole,  the 
sun  appears  to  sweep  horizontally  around  the  sky 
every  twenty-four  hours,  without   any  perceptible 


THE  EABTH.  119 

variation  in  its  distance  from  the  horizon.  It  is, 
however,  slowly  rising,  until,  on  the  21st  of  June,  it 
is  twenty-three  degrees  and  twenty-eight  minutes 
above  the  horizon,  a  little  more  than  one-fourth  of 
the  distance  to  the  zenith.  This  is  the  highest  point 
it  ever  reaches.  From  this  altitude  it  slowly  de- 
scends, its  track  being  represented  by  a  spiral  or 
screw  with  a  very  fine  thread  i  and  in  the  course  of 
three  months  it  worms  its  way  down  to  the  horizon, 
which  it  reaches  on  the  22d  of  September.  On  this 
day  it  slowly  sweeps  around  the  sky,  with  its  face 
half  hidden  below  the  icy  sea.  It  still  continues  to 
descend,  and  after  it  has  entirely  disappeared  it  is 
still  so  near  the  horizon  that  it  carries  a  Bright 
twilight  around  the  heavens  in  its  daily  circuit.  As 
the  sun  sinks  lower  and  lower,  this  twilight  grows 
gradually  fainter,  till  it  fades  away.  December  21st, 
the  sun  is  23°  28'  below  the  horizon,  and  this  is  the 
midnight  of  the  dark  polar  winter.  From  this  date 
the  sun  begins  to  ascend,  and  after  a  time  it  is  her- 
alded by  a  faint  dawn,  which  circles  slowly  around 
the  horizon,  completing  its  circuit  every  twenty-four 
hours.  This  dawn  grows  gradually  brighter,  and 
on  the  22d  of  March  the  peaks  of  ice  are  gilded 
with  the  first  level  rays  of  the  six  months  day.  The 
biinger  of  this  long  day  continues  to  wind  his  spiral 
way  upward,  till  he  reaches  his  highest  place  on  the 
21st  of  June,  and  his  annual  course  is  completed." 

XIX.  Results,  if  the  axis  of  the  earth  were  perpen- 
dicular to  the  ecliptic. — The  sun  would  then  always 


120  THE  SOLAK  SYSTEM. 

appear  to  move  through  the  equinoctial.  He  would 
rise  and  set  every  day  at  the  same  points  on  the 
horizon,  and  pass  through  the  same  circle  in  the 
heavens,  while  the  days  and  nights  would  be  equal 
the  year  round.  There  would  be  near  the  equator  a 
fierce  torrid  heat,  while  north  and  south  the  climate 
would  melt  away  into  temperate  spring,  and,  lastly, 
into  the  rigors  of  a  perpetual  winter. 

XX.  Results,  if  the  equator  of  the  earth  were  perpen- 
dicular to  the  ecliptic. — Were  this  the  case;  to  a  spec- 
tator at  the  equator,  as  the  earth  leaves  the  vernal 
equinox,  the  sun  would  each  day  pass  through  a 
smaller  circle,  until  at  the  summer  solstice  he  would 
reach  the  north  pole,  when  he  would  halt  for  a  time 
and  then  slowly  return  in  an  inverse  manner. 

In  our  own  latitude,  the  sun  would  make  his 
diurnal  revolutions  in  the  way  we  have  just  de- 
scribed, his  rays  shining  past  the  north  pole  fur- 
ther and  further,  until  we  were  included  in  the 
region  of  perpetual  day,  when  he  would  seem  to 
wind  in  a  spiral  course  up  to  the  north  pole,  and 
then  return  in  a  descending  curve  to  the  equator. 

PKECESSION  OF  THE  EQUINOXES. — We  have  spoken 
of  the  equinoxes  as  if  they  were  stationary  in  the 
orbit  of  the  earth.  Over  two  thousand  years  ago, 
Hipparchus  found  that  they  were  falling  back  along 
the  ecliptic.  Modern  astronomers  fix  the  rate  at 
about  50"  of  space  annually.  If  we  mark  either  point 
in  the  ecliptic  at  which  the  days  and  nights  are  equal 
over  the  earth,  which  is  where  the  plane  of  the  earth's 


THE  EARTH.  121 

equator  passes  exactly  through  the  centre  of  the 
sun,  we  shall  find  the  earth  the  next  year  comes 
back  to  that  position  50"  (20  m.  20  s.  of  time)  earlier. 
This  remarkable  effect  is  called  the  Precession  of  the 
Equinoxes,  because  the  position  of  the  equinoxes  in 
any  year  precedes  that  which  they  occupied  the  year 
before.  Since  the  circle  of  the  ecliptic  is  divided 
into  360°,  it  follows  that  the  time  occupied  by  the 
equinoctial  points  in  making  a  complete  revolution 
at  the  rate  of  50.2"  per  year  is  25,816  years. 

Results  of  tlie  Precession  of  the  Equinoxes. — In  Fig. 
31,  we  see  that  the  line  of  the  equinoxes  is  not 
at  right  angles  to  the  ecliptic.  In  order  that  the 
plane  of  the  terrestrial  equator  should  pass  through 
the  sun's  centre  50"  earlier,  it  is  necessary  that  the 
plane  itself  should  slightly  change  its  place.  The 
axis  of  the  earth  is  always  perpendicular  to  this 
plane,  hence  it  follows  that  the  axis  is  not  rigorously 
parallel  to  itself.  It  varies  in  direction,  so  that  the 
north  pole  describes  a  small  circle  in  the  starry 
vault  twice  23°  28'  in  diameter.  To  illustrate  this, 
in  the  cut  we  suppose  that  after  a  series  of  years  the 
position  of  the  earth's  equator  has  changed  from  efh 
to  g  K 1.  The  inclination  of  the  axis  of  the  earth,  C  P, 
to  CQ,  the  pole  of  the  ecliptic,  remains  unchanged ;  but 
as  it  must  turn  with  the  equator,  its  position  is  moved 
from  CP  to  OP',  and  it  passes  slowly  around  through 
a  portion  of  a  circle  whose  centre  is  C  Q.  The  direc- 
tion of  this  motion  is  the  same  as  that  of  the  hands 
of  a  watch,  or  just  the  reverse  of  that  of  the  revolution 

a 


122 


THE   SOLAR   SYSTEM. 


of  the  earth  itself.  The  position  of  the  north  pole  in 
the  heavens  is  therefore  gradually  but  almost  insen- 
sibly changing.  It  is  now  distant  from  the  north 
polar  star  about  1J°.  It  will  continue  to  approach 


CHANGE  OF  EARTH'S  EQUATOR  AND  AXIS. 

it  until  they  are  not  more  than  half  a  degree  apart. 
In  12,000  years  Lyra  will  be  our  polar  star :  4,50C 
years  ago  the  polar  star  was  the  bright  star  in  the 
constellation  Draco.  As  the  right  ascension  of  the 
stars  is  reckoned  eastward  from  the  vernal  equinox 
along  the  equinoctial,  the  precession  of  the  equinoxes 
increases  the  E.  A.  of  the  stars  50"  per  year.  On 
this  account,  star  maps  must  be  accompanied  by  the 
date  of  their  calculations,  that  they  may  be  corrected 
to  correspond  with  this  annual  variation.  The  con- 
stellations are  fixed  in  the  heavens,  while  the  signs  of 


THE   EARTH.  123 

the  zodiac  are  not ;  they  are  simply  abstract  divisions 
of  the  ecliptic  which  move  with  the  equinox.  When 
named,  the  sun  was  in  both  the  sign  and  constellation 
Aries,  at  the  time  of  the  vernal  equinox ;  but  since 
then  the  equinoxes  have  retrograded  nearly  a  whole 
sign,  so  that  now  while  the  sun  is  in  the  sign  Aries 
on  the  ecliptic,  it  corresponds  to  the  constellation 
Pisces  in  the  heavens.  Pisces  is  therefore  the  first 
constellation  in  the  zodiac.  (See  Fig.  72.) 

Causes  of  the  Precession  of  the  Equinoxes. — Before 
commencing  the  explanation  of  this  phenomenon,  it 
is  necessary  to  impress  upon  the  mind  a  few  facts. 
1.  The  earth  is  not  a  perfect  sphere,  but  is  swollen 
at  the  equator.  It  is  like  a  perfect  sphere  covered 
with  padding,  which  increases  constantly  in  thick- 
ness from  the  poles  to  the  equator ;  this  gives  it  a 
turnip-like  shape.  2.  The  attraction  of  the  sun  is 


INFLUENCE  OF  THE  SUN  ON  A  MOUNTAIN  NEAR  THE  EQUATOR. 

greater  the  nearer  a  body  is  to  it.  3.  The  attraction 
is  not  for  the  earth  as  a  mass,  but  for  each  particle 
separately.  In  the  figure,  the  position  of  the  earth 


124  THE  SOLAR  SYSTEM. 

at  the  time  of  the  winter  solstice  is  represented, 
P  is  the  north  pole,  a  b  the  ecliptic,  C  the  centre 
of  the  earth,  C  Q  a  line  perpendicular  to  the  eclip- 
tic, so  that  the  angle  QCP  equals  the  obliquity 
of  the  ecliptic.  In  this  position  the  equatorial  pad- 
ding we  have  spoken  of — the  ring  of  matter  about 
the  equator — is  turned,  not  exactly  toward  the 
sun,  but  is  elevated  above  it.  Now  the  attraction 
of  the  sun  pulls  the  part  D  more  strongly  than 
the  centre ;  the  tendency  of  this  is  to  bring  D 
down  to  a.  In  the  same  way  the  attraction  for  C  is 
greater  than  for  I,  so  it  tends  to  draw  C  away  from 
I,  and  as  at  the  same  time  D  tends  toward  a,  to  pull 
I  up  toward  b.  The  tendency  of  this,  one  would 
think,  would  be  to  change  the  inclination  of  the  axis 
C  P  toward  C  Q,  and  make  it  more  nearly  perpendic- 
ular to  the  ecliptic.  This  would  be  the  result  if  the 
earth  were  not  revolving  upon  its  axis.  Let  us  con- 
sider the  case  of  a  mountain  near  the  equator.  This, 
if  the  sun  did  not  act  upon  it,  would  pass  through 
the  curve  H  D  E  in  the  course  of  a  semi-revolution  of 
the  earth.  It  is  nearer  the  sun  than  the  centre  C  is ; 
the  attraction  therefore  tends  to  pull  the  mountain 
downward  and  tilt  the  earth  over,  as  we  have  just 
described;  so  the  mountain  will  pass  through  the 
curve  H/V/,  and  instead  of  crossing  the  ecliptic  at  E 
it  will  cross  at  g  a  little-  sooner  than  it  otherwise 
would.  The  same  influence,  though  in  a  less  degree, 
obtains  on  the  opposite  side  of  the  earth.  The 
mountain  passes  around  the  earth  in  a  curve  nearer 


THE  EARTH. 


125 


to  b,  and  crosses  the  ecliptic  a  little  earlier.  The 
same  reasoning  will  apply  to  each  mountain  and  tc 
all  the  protuberant  mass  near  the  equatorial  regions. 
The  final  effect  is  to  turn  slightly  the  earth's  equator 
so  that  it  intersects  the  ecliptic  sooner  than  it  would 
were  it  not  for  this  attraction.  At  the  summer  sol- 
stice the  same  tilting  motion  is  produced.  At  the 
equinoxes  the  earth's  equator  passes  directly  through 
the  centre  of  the  sun,  and  therefore  there  is  no  ten- 
dency to  change  of  position.  As  the  axis  C  P  must 
move  with  the  equator,  it  slowly  revolves,  keeping 
its  inclination  unchanged,  around  C  Q,  the  pole  of 
the  ecliptic,  describing,  in  about  26,000  years,  a 
small  circle  twice  23°  28'  in  diameter. 

Precession  illustrated  in  the  spinning  of  a  top. — This 
motion  of  the  earth's  axis  is  most  singularly  illus- 
trated in  the  spinning 
of  a  top,  and  the  more 
remarkably  because 
there  the  forces  are  of 
an  opposite  character  to 
those  which  act  on  the 
earth,  and  so  produce 
an  opposite  effect.  "We 
have  seen  that  if  the 
earth  had  no  rotation,  the 
sun's  attraction  on  the 
"  padding"  at  the  equator  would  bring  C  P  nearer 
to  C  Q,  but  that  in  consequence  of  this  rotation  tho 
effect  really  produced  is  that  CP,  the  earth's  axis, 


SPINNING  OP  A  TOP. 


126  THE  SOLAR  SYSTEM. 

slowly  revolves  around  C  Q,  the  pole  of  the  heavens,  in 
a  direction  opposite  to  that  of  rotation. 

In  Fig.  34,  let  C  P  be  the  axis  of  a  spinning  top, 
and  C  Q  the  vertical  line.  The  direct  tendency  of 
the  earth's  attraction  is  to  bring  C  P  further,  from 
C  Q  (or  to  make  the  top  fall),  and  if  the  top  were 
not  spinning  this  would  be  the  result;  but  in 
consequence  of  the  rotary  motion  the  inclination 
does  not  sensibly  alter  (until  the  spinning  is  retarded 
by  friction),  and  so  C  P  slowly  revolves  around  C  Q 
in  the  same  direction  as  that  of  rotation. 

NUTATION  (nutatio,  a  nodding). — "We  have  noticed 
the  sun  as  producing  precession ;  the  moon  has, 
however,  treble  its  influence  ;  for  although  her  mass 

is  not  s-ff.info.TnnF  Part  tnat  °f  tne  sun>  Jet  sne  *s  400 
times  nearer  and  her  effect  correspondingly  greater. 
(See  p.  168.)  The  moon's  orbit  does  not  He  par- 
allel to  the  ecliptic,  but  is  inclined  to  it.  Now 
the  sun  attracts  the  moon,  and  disturbs  it  as  he 
would  the  path  of  the  mountain  we  have  just  sup- 
posed, and  the  effect  is  the  same — viz.,  the  intersec- 
tions of  the  moon's  orbit  with  the  ecliptic  travel 
backward,  completing  a  revolution  in  about  18 
years.  During  half  of  this  time  the  moon's  orbit  is 
inclined  to  the  ecliptic  in  the  same  way  as  the 
earth's  equator  ;  during  the  other  half  it  is  inclined 
in  the  opposite  way.  In  the  former  state,  the 
moon's  attractive  tendency  to  tilt  the  earth  is  very 
small,  and  the  precession  is  slow  ;  in  the  latter,  the 
tendency  is  great,  and  precession  goes  on  rapidly. 


PATH   OF   THE   NORTH  POLE 


THE   EARTH.  127 

The  consequence  of  this  is,  that  the  pole  of  the 
earth  is  irregularly  shifted,  so 
that  it  travels  in  a  slightly 
curved  line,  giving  it  a  kinti  of 
"wabbling"  or  "  nodding"  mo- 
tion, as  shown — though  greatly 
exaggerated — in  Fig.  35.  The 
obliquity  of  the  ecliptic,  which 
we  consider  23°  28',  is  the  mean 
of  the  irregularly  curved  line  IN  THB  HEAVENS. 
and  is  represented  by  the  dotted  circle. 

Periodical  change  in  the  obliquity  of  the  ecliptic. — 
Although  it  is  sufficiently  near  for  all  general  pur- 
poses to  consider  the  obliquity  of  the  ecliptic  invari- 
able, yet  this  is  not  strictly  the  case.  It  is  subject 
to  a  small  but  appreciable  variation  of  about  46" 
per  century.  This  is  caused  by  a  slow  change  of 
the  position  of  the  earth's  orbit,  due  to  the  attraction 
of  the  planets.  The  effect  of  this  movement  is  to 
gradually  diminish  the  inclination  of  the  earth's 
equator  to  the  ecliptic  (the  obliquity  of  the  ecliptic). 
This  will  continue  for  a  time,  when  the  angle  will  as 
gradually  increase ;  the  extreme  limit  of  change 
being  only  1°  21'.  The  orbit  of  the  earth  thus 
vibrates  backward  and  forward,  each  oscillation 
requiring  a  period  of  10,000  years.  This  change 
is  so  intimately  blended,  in  its  effect  upon  the 
obliquity  of  the  ecliptic,  with  that  caused  by  pre- 
cession and  nutation,  that  they  are  only  separable 
in  theory ;  in  point  of  fact,  they  all  combine  to 


128  THE  SOLAR  SISTEM. 

produce  the  waving  motion  we  have  already  de- 
scribed. As  a  consequence  of  this  variation  in  the 
obliquity  of  the  ecliptic,  the  sun  does  not  come  as 
far  north  nor  decline  as  far  south  as  at  the  Creation, 
while  the  position  of  all  the  terrestrial  circles — 
Tropic  of  Cancer,  Capricorn,  Arctic,  etc. — is  con- 
stantly but  slowly  changing.  Besides  this,  it  tends 
to  vary  slightly  the  comparative  length  of  the 
days  and  nights,  and,  as  the  obliquity  is  now  dimin- 
ishing, to  equalize  them.  As  the  result  of  this  vari- 
ation in  the  position  of  the  orbit,  some  stars  which 
were  formerly  just  south  of  the  ecliptic  are  now 
north  of  it,  and  others  that  were  just  north  are  now 
a  little  further  north ;  thus  the  latitude  of  these 
stars  is  gradually  changing. 

Change  in  tlie  major  axis  (line  of  apsides)  of  the 
earth's  orbit. — Besides  all  the  changes  in  the  posi- 
tion of  the  earth  in  its  orbit  due  to  precession,  the 
line  connecting  the  aphelion  and  perihelion  points 
of  the  orbit  itself  is  slowly  moving.  The  conse- 
quence of  this  is  a  variation  in  the  length  of  the 
seasons  at  different  periods  of  time.  In  the  year 
4089  B.  c.,  about  the  supposed  epoch  of  the  crea- 
tion, the  earth  was  in  perihelion  at  the  autumnal 
equinox,  so  that  the  summer  and  autumn  seasons 
were  of  equal  length,  but  shorter  than  the  winter 
and  spring  seasons,  which  were  also  equal.*  In  the 

*  There  is  much  discrepancy  in  the  views  held  concerning  the 
Great  Year  of  the  astronomers,  as  it  is  often  called.  (See  14 
Weeks  in  Geology,  pp.  272-3,  note.)  The  statement  given  in  the 
text  is  that  held  by  Lockyer,  Hind  and  others.  The  terms,  it 


THE   EAETH.  129 

year  1250  A.  D.,  the  earth  was  in  perihelion  when  it 
was  at  the  winter  solstice,  December  21,  instead  of 
January  1st,  as  now ;  the  spring  quarter  was  there- 
fore equal  to  the  summer  one,  and  the  autumn 
quarter  to  the  winter  one,  the  former  being  the 
longer.  In  the  year  6589  A.  D.,  the  earth  will  be  in 
perihelion  when  it  is  at  the  vernal  equinox ;  summer 
will  then  be  equal  to  autumn  and  winter  to  spring, 
the  former  seasons  being  the  longer.  In  the  year 
11928  A.  D.,  the  earth  will  be  in  perihelion  when  it 
is  at  the  summer  solstice :  finally,  in  17267  A.  D.,  the 
cycle  will  be  completed,  and  for  the  first  time  since 
the  creation  of  man  the  autumnal  equinox  will  co- 
incide with  the  earth's  perihelion. 

PEBMANENCE  IN  THE  MIDST  OF  CHANGE. — "We  thus 
see  that  the  ecliptic  is  constantly  modifying  its  ellip- 
tical shape  ;  that  the  orbit  of  the  earth  slowly  oscil- 
lates upward  and  downward ;  that  the  north  pole 
steadily  turns  its  long  index-finger  over  a  dial  that 
marks  26,000  years ;  that  the  earth,  accurately 
poised  in  space,  yet  gently  nods  and  bows  to  the 
attraction  of  sun  and  moon.  Thus  changes  are  con- 
tinually taking  place  that  would  ultimately  entirely 
reverse  the  order  of  nature.  But  each  of  these  has 
its  bounds,  beyond  which  it  cannot  pass.  The 
promise  made  to  man  after  the  Deluge,  is  that 
"  while  the  earth  remaineth,  seed-time  and  harvest, 
and  cold  and  heat,  and  summer  and  winter,  and 

should  be  noticed,  are  applied  to  the  real  position  of  the  earth 
and  not  the  apparent  position  of  the  sun.  The  dates  are  those 
given  by  Chambers  in  his  Descriptive  Astronomy. 


130 


THE   SOLAR   SYSTEM. 


day  and  night  shall  not  cease."  The  modern  dis- 
coveries of  astronomy  prove  conclusively  that  the 
seasons  are  to  be  permanent ;  that  the  Creator, 
amid  all  these  transitions,  has  ordained  the  means 
of  carrying  out  His  promise  through  all  time. 

EEFEACTION. — The  atmosphere  extends  above  the 
earth  about  500  miles.  Near  the  surface  it  is 
dense,  while  in  the  upper  regions  it  is  exceedingly 
rare.  The  rays  of  light  from  the  heavenly  bodies 

Fig.  36. 


REFRACTION. 


passing  through  these  different  layers  are  turned 
downward  toward  a  perpendicular  more  and  more 
as  the  density  increases.  According  to  a  well- 
known  law  of  optics,  if  the  ray  of  light  from  a  star 
were  bent  in  fifty  directions  before  entering  the  eye, 
the  star  would  nevertheless  appear  to  be  in  the  line 
of  the  one  nearest  the  eye.  The  effect  of  this  is, 
that  the  apparent  place  of  a  heavenly  body  is  higher 


THE  EARTH. 


131 


than  the  true  place.  This  is  illustrated  in  Fig.  36. 
The  sun  at  S,  were  it  not  for  the  atmosphere,  would 
send  a  direct  ray  to  L.  Instead,  the  ray  at  A  is 
refracted  downward,  and  would  then  enter  the  eye 
at  N  ;  passing,  however,  through  a  layer  of  a  differ- 
ent density,  at  B  it  is  again  bent,  and  meets  the  eye 
of  the  observer  at  C.  He  sees  the  sun,  not  in  the 
direction  of  the  curved  line  C  B  A  S,  but  that  of  the 
straight  line  CBS. 

The  amount  of  refraction  varies  with  the  tempera- 
ture, moisture,  and  other  conditions  of  the  atmos- 
phere. It  is  zero  for  a  body  in  the  zenith,  and 
increases  gradually  toward  the  horizon  (as  the  thick- 
ness of  the  intervening  atmosphere  increases),  where 
it  is  about  33'. 

Fig.  37. 


Change  of  place  and  appearance  of  the  sun  and  moan. 
— The  sun  may  be  really  below  the  horizon,  and  yet 


132  THE  SOLAR  SYSTEM. 

seem  to  be  above  it.  For  example,  on  April  20, 
1837,  the  moon  was  eclipsed  before  the  sun  had 
set.  The  mean  diameter  of  both  the  sun  and  moon 
being  rather  less  than  33',  it  follows  that  when 
we  see  the  lower  edge  of  either  of  these  lumina- 
ries apparently  just  touching  the  horizon,  in  reality 
the  whole  disk  is  completely  beloiu  it,  and  would 
be  altogether  hidden  were  it  not  for  the  effect 
of  refraction.  The  day  is  consequently  materially 
lengthened. 

The  sun  and  moon  often  appear  flattened  when 
near  the  horizon.  This  is  easily  accounted  for  on 
the  principle  just  stated.  The  rays  from  the  lower 
edge  pass  through  a  denser  layer  of  the  atmosphere, 
and  are  therefore  refracted  about  4'  more  than  those 
from  the  upper  edge  :  the  effect  of  this  is  to  make 
the  vertical  diameter  appear  about  4'  less  than  the 
horizontal,  and  so  distort  the  figure  of  the  disk  into 
an  oval  shape. 

The  sun  and  moon  often  appear  larger  when  near 
the  horizon  than  when  high  in  the  sky.  This  is  not 
caused  by  refraction,  but  is  a  mere  error  of  judg- 
ment. At  the  horizon  we  compare  them  with  va- 
rious terrestrial  objects  which  lie  between  them  and 
us,  while  aloft  we  have  no  association  to  guide  us, 
and  we  are  led  to  underrate  their  size.  On  looking 
at  them  through  a  tube,  the  illusion  disappears. 
The  moon  should  naturally  appear  largest  when 
at  a  great  altitude,  as  it  is  then  at  a  less  distance 
from  us. 


THE   EARTH.  133 

The  dim  and  hazy  appearance  of  the  heavenly 
bodies  when  near  the  horizon  is  caused  not  only  by 
the  rays  of  light  having  to  pass  through  a  larger 
space  in  the  atmosphere,  but  also  by  their  travers- 
ing the  lower  and  denser  part.  The  intensity  of  the 
solar  light  is  so  greatly  diminished  by  passing 
through  the  lower  strata,  that  we  are  enabled  to 
look  upon  the  sun  at  that  time  without  being  daz- 
zled by  his  brilliant  beams. 

Twiliylit. — The  glow  of  light  after  sunset  and 
before  sunrise,  which  we  term  ttvilight,  is  caused  by 
the  refraction  and  reflection  of  the  sun's  rays  by  the 
atmosphere.  For  a  time  after  the  sun  has  truly  set, 
the  refracted  rays  continue  to  reach  the  earth ;  but 
when  these  have  ceased,  he  still  continues  to  illumi- 
nate the  clouds  and  upper  strata  of  the  air,  just  as 
he  may  be  seen  shining  on  the  summits  of  lofty 
mountains  long  after  he  has  disappeared  from  the 
view  of  the  inhabitants  of  the  plains  below.  The 
air  and  clouds  thus  illuminated  reflect  back  part 
of  the  light  to  the  earth.  As  the  sun  sinks  lower, 
less  light  reaches  us  until  reflection  ceases  and 
night  ensues.  The  same  thing  occurs  before  sun- 
rise, only  in  reverse  order.  The  duration  of  twilight 
is  usually  reckoned  to  last  until  the  sun's  depres- 
sion below  the  horizon  amounts  to  18° ;  this,  how- 
ever, varies  with  the  latitude,  seasons,  and  condi- 
tion of  the  atmosphere.  Strictly  speaking,  in  the 
latitude  of  Greenwich  there  is  no  true  night  for  a 
month  before  and  after  the  summer  solstice,  but 


134  THE   SOLAR  SYSTEM. 

constant  twilight  from  sunset  to  sunrise.  The  sun 
is  then  near  the  Tropic  of  Cancer,  and  does  not 
descend  so  much  as  18°  below  the  horizon  during 
the  entire  night.  The  twilight  is  shortest  at  the 
equator  and  longest  toward  the  poles,  where  the 
night  of  six  months  is  shortened  by  an  evening 
twilight  of  about  fifty  days  and  a  morning  one  of 
equal  length. 

Diffused  light. — The  diffused  light  of  day  is  pro- 
duced in  the  same  manner  as  that  of  twilight.  The 
atmosphere  reflects  and  scatters  the  sunlight  in 
every  direction.  "Were  it  not  for  this,  no  object 
would  be  visible  to  us  out  of  direct  sunshine  ;  every 
shadow  of  a  passing  cloud  would  be  pitchy  dark- 
ness ;  the  stars  would  be  visible  all  day ;  no  window 
would  admit  light  except  as  the  sun  shone  directly 
through  it,  and  a  man  would  require  a  lantern  to  go 
around  his  house  at  noon.  This  is  illustrated  very 
clearly  in  the  rarified  atmosphere  of  elevated  re- 
gions, as  on  Mont  Blanc,  where  it  is  said  the  glare 
of  the  direct  sunlight  is  almost  insupportable  ;  the 
darkness  of  the  shadows  is  deeper  and  denser ;  all 
nice  shading  and  coloring  disappear;  the  sky  has 
a  blackish  hue,  and  the  stars  are  seen  at  midday. 
The  blue  light  reflected  to  our  eyes  from  the  atmos- 
phere above  us,  or  more  probably  from  the  vapor  in 
the  air,  produces  the  optical  delusion  we  call  the 
sky.  Were  it  not  for  this,  every  time  we  cast  our 
eyes  upward  we  should  feel  like  one  gazing  over  a 
dizzy  precipice ;  while  now  the  crystal  dome  of  blue 


THE   EARTH.  135 

smiles  down  upon  us  so  lovingly  and  beautifully 
that  we  call  it  heaven. 

ABERRATION  OF  LIGHT. — "We  have  seen  that  the 
places  of  the  heavenly  bodies  are  apparently  changed 
by  refraction.  Besides  this,  there  is  another  change 
due  to  the  motion  of  light,  combined  with  the  mo- 
tion of  the  earth  in  its  orbit.  For  example :  the 
mean  distance  of  the  earth  from  the  sun  is  ninety- 
one  and  a  half  millions  of  miles,  and  since  light 
travels  183,000  miles  per  second,  it  follows  that  the 
time  occupied  by  a  ray  of  light  in  reaching  us  from 
the  sun  is  about  8-J  min. ;  so  that,  in  point  of  fact, 
when  we  look  at  the  sun  (1),  we  do  not  see  it  as 
it  is,  but  as  it  was  SJmin.  since.  If  our  globe 
were  at  rest,  this  would  be  well  enough,  but  since 
the  earth  is  in  motion,  when  the  ray  enters  our  eye 
we  are  at  some  distance  in  advance  of  the  position 
we  occupied  when  it  started.  During  the  SJmin. 
the  earth  has  moved  in  its  orbit  nearly  20^",  so  that 
(2)  we  never  see  that  luminary  in  the  place  it  occu- 
pies at  the  time  of  observation. 

Illustration. — Suppose  a  ball  let  fall  from  a  point 
P,  above  the  horizontal  line  A  B,  and  a  tube,  of 
which  A  is  the  lower  extremity,  placed  to  receive  it. 
If  the  tube  were  fixed,  the  ball  would  strike  it  on 
the  lower  side  ;  but  if  the  tube  were  carried  forward 
in  the  direction  A  B,  with  a  velocity  properly  ad- 
justed at  every  instant  to  that  of  the  ball,  while  pre- 
serving its  inclination  to  the  horizon,  so  that  when 
the  ball,  in  its  natural  descent,  reached  B,  the  tube 


136 


THE  SOLAR  SYSTEM. 


would  have  been  carried  into  the  position  BQ,  it  is 
evident  that  the  ball  throughout  its  whole  descent 
would  be  found  in  the  tube ;  and  a  spectator  refer- 
ring to  the  tube  the  motion  of  the  ball,  and  carried 


Fig.  38. 


ABERRATION  OP  LIGHT. 


along  with  the  former,  unconscious  of  its  motion, 
would  fancy  that  the  ball  had  been  moving  in  an 
inclined  direction,  and  had  come  from  Q.  A  very 
common  illustration  may  be  seen  almost  any  rainy 
day.  Choose  a  time  when  the  air  is  still  and  the 
drops  large.  Then,  if  you  stand  still,  you  will  .see 
that  the  drops  fall  vertically  ;  but  if  you  walk  for- 
ward, you  will  see  the  drops  fall  as  if  they  were 
meeting  you.  If,  however,  you  walk  backward,  you 
will  observe  that  the  drops  fall  as  if  they  were  com- 
ing from  behind  you.  We  thus  see  that  the  drops 
have  an  apparent  as  well  as  real  motion 


THE  EAKTH.  137 

The  general  effect  of  aberration  of  light  is  to  cause 
each  star  to  apparently  describe  a  minute  ellipse  in 
the  course  of  a  year,  the  central  point  of  which  is 
the  place  the  star  would  actually  occupy  were  our 
globe  at  rest. 

PARALLAX. — This  is  tlie  difference  in  the  direction  of 
an  object  as  seen  from  two  different  places.  For  a 
simple  illustration  of  it,  hold  your  finger  before  you 

Fig.  39. 


PARALLAX. 


in  front  of  the  window.  Upon  looking  at  it  with 
the  left  eye  only,  you  will  locate  your  linger  at  some 
point  on  the  window ;  on  looking  with  the  right  eye 
only,  you  will  locate  it  at  an  entirely  different  point. 
Use  your  eyes  alternately  and  quickly,  and  you  will 


138  THE   SOLAR  SYSTEM. 

be  astonished  at  the  rate  with  which  your  finger 
will  seem  to  change  its  place.  Now,  the  difference 
in  the  direction  of  your  finger  as  seen  from  the  two 
eyes  is  parallax. 

In  astronomical  calculations,  the  position  of  a 
body  as  seen  from  the  earth's  surface  is  called  its 
apparent  place,  while  that  in  which  it  would  be  seen 
from  the  centre  of  the  earth  is  called  its  true 
place.  Thus,  in  the  cut,  a  star  is  seen  by  the  ob- 
server at  O  in  the  direction  OP ;  if  it  could  be 
viewed  from  the  centre  R,  its  direction  would  be 
in  the  line  EQ.  It  is  therefore  seen  from  O  at  a 
point  in  the  heavens  beloiu  its  position  in  reference 
to  R.  From  looking  at  the  cut,  we  can  see  (1),  that 
the  parallax  of  a  star  near  the  horizon  is  greatest, 
while  it  decreases  gradually  until  it  disappears  alto- 
gether at  the  zenith,  since  an  observer  at  O,  as  wel] 
as  one  at  R,  would  see  the  star  Z  directly  overhead ; 
and  (2),  that  the  nearer  a  body  is  to  the  earth  the 
greater  its  parallax  becomes.  It  has  been  agreed 
by  astronomers,  for  the  sake  of  uniformity  in  their 
calculations,  to  correct  all  observations  so  as  to  refer 
them  to  their  true  places  as  seen  from  the  centre  of 
the  earth.  Tables  of  parallax  are  constructed  for 
this  purpose.  The  question  of  parallax  is  also  one 
of  very  great  importance,  because  as  soon  as  the 
parallax  of  a  body  is  once  accurately  known,  its  dis- 
tance, diameter,  etc.,  can  be  readily  determined.  (See 
Celestial  Measurements.) 

Horizontal    Parallax. — This    is    the    parallax    of 


THE  MOON.  139 

a  body  when  at  the  horizon.  It  is,  in  fact,  the 
earth's  semi-diameter  as  seen  from  the  body.  In  the 
figure,  the  parallax  of  the  star  S  is  the  angle  OSR, 
which  is  measured  by  the  line  OK — the  semi-diam- 
eter of  the  earth.  The  sun's  horizontal  parallax 
(8.94")  is  the  angle  subtended  (measured)  by  the 
earth's  semi-diameter  as  seen  from  that  luminary. 
As  the  moon  is  nearest  the  earth,  its  horizontal  par- 
allax is  the  greatest  of  any  of  the  heavenly  bodies. 

Annual  Parallax. — The  fixed  stars  are  so  distant 
from  the  earth  that  they  exhibit  no  change  of  place 
when  seen  from  different  parts  of  the  earth.  The 
lines  OS  and  US  are  so  long  that  they  are  ap- 
parently parallel,  and  it  becomes  impossible  to 
discover  the  slightest  inclination.  Astronomers, 
therefore,  instead  of  taking  the  earth's  semi-diam- 
eter, or  4,000  miles,  as  the  measuring  tape,  have 
adopted  the  plan  of  observing  the  position  of  the 
fixed  stars  at  opposite  points  in  the  earth's  orbit. 
This  gives  a  change  in  place  of  183,000,000  miles. 
The  variation  of  position  which  the  stars  under- 
go at  these  remote  points  is  called  their  annual 
parallax. 

THE  MOON. 

New  Moon,  •.    First  Quarter,  ®.    Full  Moon,  ©.    Last  Quarter,  «>. 

ITS  MOTION  IN  SPACE. — The  orbit  of  the  moon,  con- 
sidering the  earth  as  fixed,  is  an  ellipse  of  which  our 
planet  occupies  one  of  the  foci.  Its  distance  from 


140 


THE   SOLAR   SYSTEM. 


the  earth  therefore,  varies  incessantly.  At  perigee 
it  is  26,000  miles  nearer  than  in  apogee  :  the  mean 
distance  is  about  238,000  miles.  It  would  require  a 
chain  of  thirty  globes  equal  in  size  to  the  earth  to 
reach  the  moon.  An  express-train  would  take  about 
a  year  to  accomplish  the  journey.  The  moon  com  • 
pletes  its  revolution  (sidereal)  around  the  earth  in 
about  27i  days ;  but,  as  the  earth  is  constantly  pass- 
Fig.  40. 


PATH  OP  MOON. 


ing  on  in  its  own  orbit  around  the  sun,  it  requires 
over  two  days  longer  before  it  comes  into  the  same 
position  with  respect  to  the  sun  and  earth,  thus  com- 
pleting its  synodic  revolution. 


THE  MOON.  141 

The  real  path  of  the  moon  is  the  result  of  its  own 
proper  motion  and  the  onward  movement  of  the 
earth.  The  two  combined  produce  a  wave-like 
curve  that  crosses  the  earth's  path  twice  each 
month ;  this,  owing  to  its  small  diameter  com- 
pared with  that  of  the  ecliptic,  is  always  concave 
toward  the  sun.  As  the  moon  constantly  keeps 
the  same  side  turned  toward  us,  it  follows  that 
it  must  turn  on  its  axis  once  each  month. 

DIMENSIONS. — Its  diameter  is  about  2,160  miles. 
It  would  require  fifty  globes  the  size  of  the  moon  to 
equal  the  earth.  Its  apparent  size  varies  with  its 
distance ;  the  mean  is,  however,  about  one  half  a 

Pig.  41. 


THE  SIZE  OP  MOON  AT  HORIZON  AND  ZENITH. 

degree,  the  same  as  that  of  the  sun.  It  always  ap- 
pears larger  than  it  really  is,  on  account  of  its 
brightness.  This  is  the  effect  of  what  is  termed  in 
optics  Irradiation.  To  illustrate  this  principle,  cut 
two  circular  pieces  of  the  same  size,  one  of  black 


THE   80LAE   SYSTEM. 

/the  other  of  white  paper.  The  white  circle, 
en  held  in  a  bright  light,  will  appear  much  larger 
than  the  black  one.  For  the  same  reason  it  is  often 
noticed  that  the  crescent  moon  seems  to  be  a  part  of 
a  larger  circle  than  the  rest  of  the  moon.  As  we 
have  already  said,  the  moon  appears  larger  on  the  ho- 
rizon than  when  high  up  in  the  sky.  By  an  examina- 
tion of  the  cut,  it  is  easily  seen  that  it  is  4,000  miles 
nearer  when  on  the  zenith  than  when  at  the  horizon. 
Besides  these  general  variations  in  size,  the  moon 
varies  in  apparent  size  to  different  observers.  Much 
amusement  may  be  had  in  a  large  party  or  class  by 
a  comparison  of  its  apparent  magnitude.  The  esti- 
mates will  differ  from  a  small  saucer  to  a  wash-tub. 

LIBKATIONS  (librans,  swinging). — "While  the  moon 
presents  the  same  hemisphere  to  us,  there  are  three 
causes  which  enable  us  to  see  about  576  out  of  the 
1,000  parts  of  its  entire  surface.  (1.)  The  axis  of 
the  moon  is  inclined  a  little  to  its  orbit,  as  also  its 
orbit  is  inclined  to  the  earth's  orbit;  so  when  its 
north  pole  leans  alternately  toward  and  from  the 
earth,  we  see  sometimes  past  its  north,  and  some- 
times past  its  south  pole.  This  is  called  libration  in 
latitude.  (2.)  The  moon's  rotation  on  its  axis  is  al- 
ways performed  in  the  same  time,  while  its  move- 
ment along  its  orbit  is  variable  ;  hence  it  happens 
that  we  occasionally  see  a  little  further  around  each 
limb  (outer  edge)  than  at  other  times.  This  is  called 
libration  in  longitude.  (3.)  The  size  of  the  earth  is 
so  much  greater  than  that  of  the  moon,  that  an  ob- 


THE   MOON.  143 

server,  by  the  rotation  of  the  earth,  or  by  going 
north  or  south,  can  see  further  around  the  limbs. 

LIGHT  AND  HEAT. — If  the  whole  sky  were  covered 
with  full  moons,  they  would  scarcely  make  daylight, 
since  the  brilliancy  of  the  moon  does  not  exceed 
sir^Tnnj- tnat  °f tne  sun-  That  portion  of  the  moon's 
surface  which  is  exposed  to  the  sun  is  supposed 
to  be  highly  heated,  possibly  to  the  degree  of  boil- 
ing water,  yet  its  rays  impart  no  heat  to  us ;  indeed 
Prof.  Tyndall  considers  them  rays  of  cold.  This  is 
probably  caused  by  the  fact  that  our  dense  atmos- 
phere absorbs  all  the  heat,  which  in  the  higher  re- 
gions produces  the  effect  of  scattering  the  clouds. 
It  is  a  well-known  fact  that  the  nights  are  oftenest 
clear  at  full  moon.  (Herschel.) 

CENTEE  OF  GRAVITY. — It  is  thought  that  the  centre 
of  gravity  of  the  moon  is  not  exactly  at  its  centre 
of  magnitude,  but  nearly  thirty-three  miles  beyond, 
and  that  the  lighter  half  is  toward  us.  If  that  be 
so,  this  side  is  equivalent  to  a  mountain  of  that 
enormous  height.  We  can  easily  see  that  if  water 
and  air  exist  upon  the  moon,  they  cannot  remain  on 
this  hemisphere,  but  must  be  confined  to  the  side 
which  is  forever  hidden  from  our  view. 

ATMOSPHERE  OF  THE  MOON. — The  existence  of  an 
atmosphere  upon  our  satellite  is  at  present  an  open 
question.  If  there  be  any,  it  must  be  extremely 
rarefied,  perhaps  as  much  so  as  that  which  is  found 
in  the  vacuum  obtained  in  the  receiver  of  our  best 
air-pumps. 


144 


THE  SOLAR  SYSTEM. 


Pig.  42. 


APPEARANCE  OF  THE  EARTH  TO  LUNARIANS.— If  tlieie 
be  any  lunar  inhabitants  on  the  side  toward  us,  the 
earth  must  present  to  them  all  the  phases  which 
their  world  exhibits  to  us,  only  in  a  reverse  order. 
When  we  have  a  new  moon,  they  have  a  futt  earth, 
a  bright  full-orbed 
moon  fourteen  times 
as  large  as  ours.  The 
lunar  inhabitants  upon 
the  side  opposite  to  us 
of  course  never  see  our 
earth,  unless  they  take 
a  journey  to  the  re- 
gions from  whence  it 
is  visible,  to  behold 
this  wonderful  spec- 
tacle. Those  living 
near  the  limbs  of  the  disk  might,  however,  on  ac- 
count of  the  librations,  get  occasional  glimpses  of  it 
near  their  horizon. 

THE  EARTH-SHINE. — For  a  few  days  before  and 
after  new  moon,  we  may  distinguish  the  outline  of 
the  unillumined  portion  of  the  moon.  In  England, 
it  is  popularly  known  as  "  the  old  moon  in  the  new 
moon's  arms."  This  reflection  of  the  earth's  rays 
must  serve  to  keep  the  lunar  nights  quite  light, 
even  in  new  earth. 

PHASES  OF  THE  MOON. — The  phases  of  the  moon 
show  conclusively  that  it  is  a  dark  body,  which 
shines  only  by  reflecting  the  light  it  receives  from 


APPEARANCE  OP  EARTH  AS  SEEN  FROM 
MOON. 


THE   MOON. 


145 


the  sun.     Let  us  compare  its  various  appearances 
with  the  positions  indicated  in  the  figure. 


Fig.  43. 


PHASES   OF   MOON. 


We  see  it  (1)  as  a  delicate  crescent  in  the  west 
just  after  sunset,  as  it  first  emerges  from  the  sun's 

7 


146  THE   SOLAR   SYSTEM. 

rays  at  conjunction.  It  soon  sets  below  the  horizon 
Half  of  its  surface  is  illumined,  but  only  a  slender 
edge  with  its  horns  turned  from  the  sun  is  visible  to 
us.  Each  night  the  crescent  broadens,  the  moon 
recedes  about  13°  further  from  the  sun,  and  sets  cor- 
respondingly later,  until  at  quadrature  half  of  the 
enlightened  hemisphere  is  turned  toward  us,  and  the 
moon  is  said  to  be  in  her  first  quarter.  Continuing 
her  eastern  progress  round  the  earth,  the  moon  (2) 
becomes  gibbous*  in  form,  and,  about  the  fifteenth 
day  from  new  moon,  reaches  the  point  in  the  heavens 
directly  opposite  to  that  which  the  sun  occupies. 
She  is  then  in  opposition,  the  whole  of  the  illumined 
side  is  turned  toward  us,  and  we  have  a  full  moon. 
She  is  on  the  meridian  at  midnight,  and  so  rises  in 
the  east  as  the  sun  sets  in  the  west,  and  vice  versa. 

The  moon  (3)  passing  on  in  her  orbit  from  oppo- 
sition, presents  phases  reversed  from  those  of  the  sec- 
ond quarter.  The  proportion  of  the  illumined  side 
visible  to  us  gradually  decreases ;  she  becomes  gibbous 
again ;  rises  nearly  an  hour  later  each  evening,  and 
in  the  morning  lingers  high  in  the  western  sky  after 
sunrise.  She  now  comes  into  quadrature,  and  is  in 
her  third  quarter. 

From  the  third  quarter  the  moon  (4)  turns  her  en- 
lightened side  from  us  and  decreases  to  the  crescent 
form  again;  as,  however,  the  bright  hemisphere 


*  (jitibw*  means  less  than  a  half  and  more  than  a  quarter 
circle. 


THE   MOON.  147 

constantly  faces  the  sun,  the  horns  are  pointed 
toward  the  west.  She  is  now  seen  as  a  bright  cres- 
cent in  the  eastern  sky  just  before  sunrise.  At  last 
the  illumined  side  is  completely  turned  from  us,  and 
the  moon  herself,  coming  into  conjunction  with  the 
sun,  is  lost  in  his  rays.  To  accomplish  this  journey 
through  her  orbit  from  new  moon  to  new  moon,  has 
required  29J  days — a  lunar  month. 

Moon  runs  high  or  low. — All  have,  doubtless,  no- 
ticed that,  in  the  long  nights  of  winter,  the  full  moon 
is  high  in  the  heavens,  and  continues  a  long  time 
above  the  horizon;  while  in  midsummer  it  is  low, 
and  remains  a  much  shorter  time  above  the  horizon. 
This  is  a  wise  provision  of  Providence,  which  is  seen 
yet  more  clearly  in  the  arctic  regions.  There  the 
moon;  during  the  long  summer  day  of  six  months,  is 
above  the  horizon  only  for  her  first  and  fourth  quar- 
ters, when  her  light  is  least ;  but  during  the  tedious 
winter  night  of  equal  length,  she  is  continually  above 
the  horizon  for  her  second  and  third  quarters.  Thus 
in  polar  regions  the  moon  is  never  full  by  day,  but 
is  always  full  every  month  in  the  night.  We  can 
easily  understand  these  phenomena  when  we  remem- 
ber that  the  new  moon  is  in  the  same  quarter  and 
the  full  moon  in  the  opposite  quarter  of  the  heavens 
from  the  sun.  Consequently,  the  moon  always  be- 
comes full  in  the  other  solstice  from  that  in  which 
the  sun  is.  When,  therefore,  the  sun  sinks  very 
low  in  the  southern  sky  the  full  moon  rises  high, 
and  when  the  sun  rises  high  the  full  moon  sinks  low. 


148  THE   SOLAR   SYSTEM. 

HARVEST  MOON. — While  the  moon  rises  on  the 
average  50  m.  later  each  night,  the  exact  time  va- 
ries from  less  than  half  an  hour  to  a  full  hour. 
Near  the  time  of  autumnal  equinox  the  moon,  at 
her  full,  rises  about  sunset  a  number  of  nights  in 
succession.  This  gives  rise  to  a  series  of  brilliant 
moonlight  evenings.  It  is  the  time  of  harvest  in 
England,  and  hence  has  received  the  name  of  the 
Harvest  Moon.  Its  return  is  celebrated  as  a  festi- 
val among  the  peasantry.  In  the  following  month 
(October)  the  same  occurrence  takes  place,  and  it  is 
then  termed  the  Hunter's  Moon.  The  cause  of  this 
phenomenon  lies  in  the  fact  that  the  moon's  path  is 
variously  inclined  to  the  horizon  at  different  seasons 
of  the  year.  When  the  equinoxes  are  in  the  hori- 
zon, it  makes  a  very  small  angle  with  the  horizon  ; 
whereas,  when  the  solstitial  points  are  in  the  horizon, 
the  angle  is  far  greater.  In  the  former  case,  the 
moon  moving  eastward  each  day  about  13°,  will  de- 
scend but  little  below  the  horizon,  and  so  for  sev- 
eral successive  evenings  will  rise  at  about  the 
same  hour.  In  the  latter,  glie  will  descend  much 
further  each  day  and  thus  will  rise  much  later  each 
night.  The  least  possible  variation  in  the  hour  of 
rising  is  17  minutes — the  greatest  is  1  hour,  16 
minutes. 

In  the  figure,  S  represents  the  sun,  E  the  earth, 
M  the  moon  ;  C  F  the  moon's  path  around  the  earth 
\vhen  the  solstitial  points  are  in  the  horizon — E  D 
when  the  equinoxes  are  in  the  horizon ;  A  M  B  S  the 


THE  MOON. 


149 


Fig.  44. 


horizon ;  M.d  =  M.b  =13°,  the  distance  the  moon 
moves  each  day.  When  passing  along  the  path  G  F, 
the  moon  sinks  below  the  horizon  the  distance  al, 
and  when  mov- 
ing along  the 
path  E  D,  only 
the  distance 
cd.  It  is  ob- 
vious that  be- 
fore the  moon  j±\ 
can  rise  in  the 
former  case, 
the  horizon 
must  be  de- 
pressed the 
distance  a  I, 
and  in  the  lat- 
ter only  cd;  and  the  moon  will  rise  correspondingly 
later  in  the  one  and  earlier  in  the  other. 

NODES. — The  orbit  of  the  moon  is  inclined  to  the 
ecliptic  about  5°,  the  points  where  her  path  crosses 
it  being  termed  nodes.  The  ascending  node  (&)  is 
the  place  where  the  moon  crosses  in  coming  above 
the  ecliptic  or  toward  the  north  star ;  the  descending 
node  (8)  is  where  it  passes  below  the  ecliptic.  The 
imaginary  line  connecting  these  two  points  is  called 
the  "  line  of  the  nodes." 

OCCULTATION. — The  moon,  in  the  course  of  her 
monthly  journey  round  the  earth,  frequently  passes 
in  front  of  the  stars  or  planets,  which  disappear  on 


HARVEST   MOON. 


150  THE  SOLAR  SYSTEM. 

one  side  of  her  disk  and  reappear  on  the  other, 
This  is  termed  an  occultation,  and  is  of  practical  use 
in  determining  the  difference  of  longitude  between 
various  places  on  the  earth. 

LUNAR  SEASONS;  DAY  AND  NIGHT,  ETC. — As  the 
moon's  axis  is  so  nearly  perpendicular  to  her  orbit, 
she  cannot  properly  be  said  to  have  any  change  of 
seasons.  During  nearly  fifteen  of  our  days,  the  sun 
pours  down  its  rays  unmitigated  by  any  atmosphere 
to  temper  them.  To  this  long,  torrid  day  succeeds  a 
night  of  equal  length  and  polar  cold.  How  strange 
the  lunar  '  appearance  would  be  to  us !  The  disk  of 
the  sun  seems  sharp  and  distinct.  The  sky  is 
black  and  overspread  with  stars  even  at  midday. 
There  is  no  twilight,  for  the  sun  bursts  instantly 
into  day,  and  after  a  fortnight's  glare,  as  suddenly 
gives  place  to  night;  no  air  to  conduct  sound,  no 
clouds,  no  winds,  no  rainbow,  no  blue  sky,  no  gor- 
geous tinting  of  the  heavens  at  sunrise  and  sunset, 
no  delicate  shading,  no  soft  blending  of  colors,  but 
only  sharp  outlines  of  sun  and  shade. 

What  a  bleak  waste !  A  barren,  voiceless  desert ! 
The  nights,  however,  of  the  visible  hemisphere  must 
be  brilliantly  illuminated  by  the  earth,  while  its 
phases  "  serve  well  as  a  clock — a  dial  all  but  fixed 
in  the  same  part  of  the  heavens,  like  an  immense 
lamp,  behind  which  the  stars  slowly  defile  along  the 
black  sky." 

TELESCOPIC  FEATURES. — The  lunar  landscape  is 
yet  more  wonderful  than  its  other  physical  features 


THE   MOON. 
Pi*.  45. 


151 


EAT,  LANDSCAPE  OF  THK  MOON. 


152  THE   SOLAR   SYSTEM. 

Even  with  the  naked  eye  we  see  on  its  surface  bright 
spots — the  summits  of  lofty  mountains,  gilded  by 
the  first  rays  of  the  sun — and  darker  portions,  low 
plains  yet  lying  in  comparative  shadow.  The  tele- 
scope reveals  to  us  a  region  torn  and  shattered  by 
fearful,  though  now  extinct*  volcanic  action.  Every- 
where the  crust  is  pierced  by  craters,  whose  irregu 
lar  edges  and  rents  testify  to  the  convulsions  our 
satellite  has  undergone  at  some  past  time. 

Mountains. — The  heights  of  more  than  1,000  of 
these  lunar  mountains  have  been  measured,  some  of 
which  exceed  20,000  feet.  The  shadows  of  the 
mountains,  as  the  sun's  rays  strike  them  obliquely, 
are  as  distinctly  perceived  as  that  of  an  upright 
staff  when  placed  opposite  the  sun.  Some  of  these 
are  insulated  peaks  that  shoot  up  solitary  and  alone 
from  the  centre  of  circular  plains  ;  others  are  moun- 
tain ranges  extending  hundreds  of  miles.  Most  of 
the  lunar  elevations  have  received  names  of  men 
distinguished  in  science.  Thus  we  find  jPlato,  Aris- 
tarchus,  Copernicus,  Kepler,  and  Newton,  associated 
however  with  the  Apennines,  Carpathians,  etc. 

Gray  plains  or  seas. — These  are  analogous  to  our 
prairies.  They  were  formerly  supposed  to  be  sheets 
of  water,  but  have  more  recently  been  found  to  ex- 


*  Several  distinguished  astronomers  assert,  however,  that  the 
crater  Linnaeus  has  undergone  of  late  certain  marked  changes. 
Its  sides  seem  to  have  fallen  in,  and  the  interior  to  have  become 
filled  up,  as  if  by  a  new  eruption.  It  is  said  to  present  an  ap- 
pearance similar  to  that  of  the  Sea  of  Serenity. 


154  THE  SOLAR  SYSTEM. 

hibit  the  uneven  appearances  of  a  plain,  instead  of 
the  regular  curve  of  bodies  of  water.  The  former 
names  have  been  retained,  and  we  find  on  lunar 
maps  the  "  Sea  of  Tranquillity,"  the  "  Sea  of  Nee- 
tar,"  "  Sea  of  Serenity,"  etc. 

Rills,  luminous  bands. — The  latter  are  long  bright 
streaks,  irregular  in  outline  and  extent,  which  radi- 
ate in  every  direction  from  Tycho,  Kepler,  and  other 
mountains ;  the  former  are  similar,  but  are  sunken, 
and  have  sloping  sides,  and  were  at  first  thought  to 
be  ancient  river-beds.  Their  exact  nature  is  yet  a 
mystery. 

Craters. — These  constitute  by  far  the  most  curious 
feature  of  the  lunar  landscape.  They  are  of  volcanic 
origin,  and  usually  consist  of  a  cup-like  basin,  with  a 
conical  elevation  in  the  centre.  Some  of  the  craters 
have  a  diameter  of  over  100  miles.  They  are  great 
walled  plains,  sunk  so  far  behind  huge  volcanic  ram- 
parts, that  the  lofty  wall  which  surrounds  an  ob- 
server at  the  centre  would  be  beyond  his  horizon. 
Other  craters  are  deep  and  narrow, — as  Newton, 
which  is  said  to  be  about  four  miles  in  depth, — 
so  that  neither  earth  nor  sun  is  ever  visible  from  a 
great  part  of  the  bottom.  The  appearance  of  these 
craters  is  strikingly  shown  in  the  accompanying 
view  of  the  region  to  the  southeast  of  Tycho.  (Fig. 
46.) 


ECLIPSES. 


155 


ECLIPSES. 

ECLIPSE  OF  THE  SUN. — If  the  moon  should  pass 
through  either  node  at  or  near  the  time  of  conjunc- 
tion or  neiv  moon,  she  would  necessarily  come  be- 
tween the  earth  and  the  sun,  for  the  three  bodies 
are  then  in  the  same  straight  line.  This  would  cause 


Fig.  47. 


of  &* 


ECLIPSE  OP  SUN. 


an  eclipse  of  the  sun.  If  the  moon's  orbit  were  in 
the  same  plane  as  the  ecliptic,  an  eclipse  of  the  sun 
would  occur  at  every  new  moon ;  but  as  the  orbit  is 
inclined,  it  can  occur  only  at  or  near  a  node. 

The  eclipse  may  be  partial,  total,  or  annular. — In 
Fig.  48,  we  see  where  the  dark  shadow  (umbra)  of 

Fig.  48 


UMBRA   AND  PENUMBRA. 


the  moon  falls  on  the  earth  and  obscures  the  entire 
body  of  the  sun.     To  the  persons  within  that  region 


156  THE   SOLAR  SYSTEM. 

there  is  a  total  eclipse;  the  breadth  of  this  space 
is  not  large,  averaging  only  140  miles.  Beyond 
this  umbra  there  is  a  lighter  shadow,  penumbra 
(pene,  almost  -  —  umbra,  a  shadow),  where  only  a 
portion  of  the  sun's  disk  is  obscured.  Within  this 
region  there  is  a  partial  eclipse.  To  those  persons  liv- 
ing north  of  the  equator  and  of  the  umbra,  the  eclipse 
passes  over  the  lower  limb  of  the  sun ;  to  those 
south  of  the  umbra,  it  passes  over  the  upper  limb.* 
When  the  eclipse  occurs  exactly  at  the  node,  it  is  said 
to  be  central.  If  the  eclipse  takes  place  when  the  moon 
is  at  apogee,  or  furthest  from  the  earth,  her  apparent 
diameter  is  less  than  that  of  the  sun ;  as  a  conse- 
quence, her  disk  does  not  cover  the  disk  of  the  sun, 
and  the  visible  portions  of  that  luminary  appear  in 
the  form  of  a  ring  (annulus) ;  hence  there  is  an  an- 
nular eclipse  in  all  those  places  comprised  within  the 
limits  of  the  cone  of  shadow  prolonged  to  the  earth. 

General  facts  concerning  a  solar  eclipse. — The  fol- 
lowing data  may  perhaps  guide  in  better  under- 
.  standing  the  phenomena  of  solar  eclipses. 

(1.)  The  moon  must  be  new. 

(2.)  She  must  be  at  or  near  a  node. 

(3.)  When  her  distance  from  the  earth  is  less  than 
the  length  of  her  shadow,  the  eclipse  will  be  total 
or  partial. 

(4.)  When  her  distance  is  greater  than  the  length 
of  her  shadow,  the  eclipse  will  be  annular  or  partial. 

(5.)  There  can  be  no  eclipse  at  those  places  where 
the  sun  himself  is  invisible  during  the  time. 

*  South  of  the  equator  the  reverse  of  these  phenomena  would 
happen. 


ECLIPSES.  15V 

(6.)  An  eclipse  is  not  visible  over  the  whole  illu- 
mined side  of  the  earth.  As  the  moon's  diameter 
is  so  much  less  than  that  of  the  earth,  her  cone  of 
shadow  is  too  small  to  enshroud  the  entire  globe,  so 
that  the  region  in  which  it  is  total  cannot  exceed 
180  miles  in  breadth.  As,  however,  the  earth  is  con- 
stantly revolving  on  its  axis  during  the  duration  of 
the  eclipse,  the  shadow  may  travel  over  a  large  sur- 
face of  territory. 

(7.)  If  the  moon's  shadow  fall  upon  the  earth 
when  she  is  just  nearing  her  ascending  node,  it  will 


Fiff.  49 


SOLAR   ECLIPTIC  LIMIT  (17°). 

only  sweep  across  the  south  polar  regions  :  if  when 
nearing  her  descending  node,  it  will  graze  the  earth 
near  the  north  pole.  The  nearer  a  node  the  con- 
junction occurs,  the  nearer  the  equatorial  regions 
the  shadow  will  strike. 

(8.)  At  the  equator,  the  longest  possible  duration 
of  a  total  solar  eclipse  is  only  about  eight  minutes, 
and  of  an  annular,  twelve  minutes.  One  reason  of  the 
greater  length  of  the  latter  is,  that  then  the  moon 
is  in  apogee,  when  it  always  moves  slower  than 
when  in  perigee.  The  duration  of  total  obscuration 
is  greatest  when  the  moon  is  in  perigee  and  the  sun 
in  apogee ;  for  then  the  apparent  size  of  the  moon 
is  greatest  and  that  of  the  sun  least.  We  see  from 


158 


TilE   SOLAR  SYSTEM. 


this  that  the  relative  situation  of  the  moon  and  sun 
decides  the  length  and  kind  of  the  eclipse. 

(9.)  There  cannot  be  more  than  five  nor  less 
than  two  solar  eclipses  per  year.  A  total  or  an  an- 
nular eclipse  is  exceedingly  rare.  For  instance, 
there  has  not  been  a  total  eclipse  visible  at  London 
since  1715,  and  previous  to  that,  there  had  been 
none  visible  for  five  and  a  half  centuries. 

(10.)  A  solar  eclipse  comes  on  the  western  limb 
or  edge  of  the  sun  and  passes  off  on  the  eastern. 

(11.)  The  disk  of  the  sun  and  moon  is  divided  into 
twelve  digits,  and  the  amount  of  the  eclipse  is  esti- 
mated by  the  number  of  digits  which  it  covers.  Thus 
an  eclipse  of  six  digits  is  one  in  which  half  the  di- 
ameter of  the  disk  is  concealed. 

Curious  phenomena. — Various  singular  appearances 
always  attend  a  total  eclipse.  Around  the  sun  is 
seen  a  beautiful  Fig.  50. 

corona  or  halo 
of  light,  like 
that  which  paint- 
ers give  to  the 
head  of  the 
Virgin  Mary. 
Flames  of  a 
blood-red  color 
play  around  the 
disk  of  the  moon, 
and  when  only 
a  mere  crescent 
of  the  sun  is  BottpsE  OF  isss 


ECLIPSES. 


159 


Fig.  51. 


visible,  it  seems  to  resolve  itself  into  bright  spots 
interspersed  with  dark  spaces,  having  the  appear- 
ance of  a  string 
of  bright  beads 
(Baily's  Beads.) 
Attendant  cir- 
cumstances of  a 
total  eclipse. — 
These  are  of  a 
peculiarly  im- 
pressive charac- 
ter. The  dark- 
ness is  so  intense 
that  the  brighter 
stars  and  planets 
are  seen,  birds 
cease  their  songs 
and  fly  to  their  nests,  flowers  close,  and  the  face  of 
nature  assumes  an  unearthly  cadaverous  hue,  while 
a  sudden  fall  of  the  temperature  causes  the  air  to 
feel  damp,  and  the  grass  wet  as  if  from  excessive 
dew.  Orange,  yellow,  and  copper  tints  give  every 
object  a  strange  appearance,  and  startle  even  the 
most  indifferent.  The  ancients  regarded  a  total 
eclipse  with  feelings  of  indescribable  terror,  as  an 
indication  of  the  anger  of  an  offended  Deity,  or  the 
presage  of  some  impending  calamity.  Even  now, 
when  the  causes  are  fully  understood,  and  the  time 
of  the  eclipse  can  be  predicted  within  the  fraction 
of  a  second,  the  change  from  broad  daylight  to  in- 


ANNULAR  ECLIPSE   OP  183&     SHOWING  BAILY'd 
BEADS. 


1GO  THE  SOLAR  SYSTEM. 

stantaneous  gloom  is  overwhelming,  and  inspires 
with  awe  even  the  most  careless  observer. 

Curious  custom  among  the  Hindoos. — Among  the 
Hindoos  a  singular  custom  is  said  to  exist.  When, 
during  a  solar  eclipse,  the  black  disk  of  our  satellite 
begins  slowly  to  advance  over  the  sun,  the  natives 
believe  that  some  terrific  monster  is  gradually  de- 
vouring it.  Thereupon  they  beat  gongs,  and  rend 
the  air  with  most  discordant  screams  of  terror  and 
shouts  of  vengeance.  For  a  time  their  frantic  efforts 
seem  futile  and  the  eclipse  still  progresses.  At 
length,  however,  the  increasing  uproar  reaches  the 
voracious  monster ;  he  appears  to  pause,  and  then, 
like  a  fish  rejecting  a  nearly  swallowed  bait,  grad- 
ually disgorges  the  fiery  mouthful.  When  the  sun 
is  quite  clear  of  the  great  dragon's  mouth,  a  shout 
of  joy  is  raised,  and  the  poor  natives  disperse,  ex- 
tremely self-satisfied  on  account  of  having  so  suc- 
cessfully relieved  their  deity  from  his  late  peril. 

THE  SAROS. — The  nodes  of  the  moon's  orbit  are 
constantly  moving  backward.  They  complete  a  rev- 
olution around  the  ecliptic  in  about  eighteen  and 
a  half  years.  Now  the  moon  makes  223  synodic 
revolutions  in  18  yr.  10  da. ;  the  sun  makes  19  rev- 
olutions with  regard  to  the  lunar  nodes  in  about  the 
same  time.  Hence,  in  that  period  the  sun  and 
moon  and  the  nodes  will  be  in  nearly  the  same  rela- 
tive position.  If,  then,  we  reckon  18  yr.  10  da.  from 
any  eclipse,  we  shall  find  the  time  of  its  repetition. 
This  method  was  discovered,  it  is  said,  by  the  dial- 


ECLIPSES.  161 

deans.  The  ancients  were  enabled,  by  means  of  it, 
to  predict  eclipses,  but  it  is  considered  too  rough  by 
modern  astronomers  :  eclipses  are  now  foretold  cen- 
turies in  advance,  true  to  a  second.  In  this  manner 
historical  incidents  are  verified,  and  their  exact  dates 
determined. 

METONIC  CYCLE. — The  Metonic  Cycle  (sometimes 
confounded  with  the  Saros)  was  not  used  for  foretell- 
ing eclipses,  but  for  the  purpose  of  ascertaining  the 
age  of  the  moon  at  any  given  period.  It  consists  of 
nineteen  tropical  years,*  during  which  time  there 
are  exactly  235  new  moons ;  so  that,  at  the  end  of 
this  period,  the  new  moons  will  recur  at  seasons  of 
the  year  exactly  corresponding  to  those  of  the  pre- 
ceding cycle.  By  registering,  therefore,  the  exact 
days  of  any  cycle  at  which  the  new  or  full  moons 
occur,  such  a  calendar  shows  on  what  days  these 
events  will  occur  in  succeeding  cycles.  Since  the 
regulation  of  games,  feasts,  and  fasts  has  been 
made  very  extensively,  both  in  ancient  and  modern 
times,  according  to  new  or  full  moons,  such  a  calen- 
dar becomes  very  convenient  for  finding  the  day  on 
which  the  new  or  full  moon  required  takes  place. 
Thus  if  a  festival  were  decreed  to  be  held  in  any 
given  year  on  the  day  of  the  first  full  moon  after 
the  vernal  equinox :  find  what  year  it  is  of  the 
lunar  cycle,  then  refer  to  the  corresponding  year  of 


*  A  tropical  year  is  the  interval  between  two  successive  retums 
of  the  sun  to  the  vernal  equinox. 


162  THE   SOLAlt  SYSTEM. 

the  preceding  cycle,  and  the  day  will  be  the  same  aa 
it  was  then.  The  Golden  Number,  a  term  still  used 
in  our  almanacs,  denotes  the  year  of  the  lunar  cycle. 
Seven  is  the  golden  number  for  1868. 

ECLIPSE  OF  THE  MOON. — This  is  caused  by  the 
passing  of  the  moon  into  the  shadow  of  the  earth, 

Fig.  52. 


ECLIPSE  OF  THE  MOON. 


and  hence  can  take  place  only  at  full  moon — oppo- 
sition. As  the  moon's  orbit  is  inclined  to  the  ecliptic, 
her  path  is  partly  above  and  partly  below  the  earth's 
shadow ;  thus  an  eclipse  of  the  moon  can  take  place 
only  at  or  near  one  of  the  nodes.  In  the  figure,  the 
umbra  is  represented  by  the  space  between  the  lines 
K  c  and  I  b ;  outside  of  this  is  the  penumbra,  where  the 
earth  cuts  off  the  light  of  only  a  portion  of  the  sun.  The 
moon  enters  the  penumbra  of  the  earth  at  a, — this  is 
termed  her  first  contact  with  the  penumbra  ;  next  she 
encounters  the  dark  shadow  of  the  earth  at  b, — this  is 
called  ike  first  contact  with  the  umbra  ;  she  then  emerges 
from  the  umbra  at  c, — which  is  called  the  second  con- 
tact  with  the  umbra ;  finally,  she  touches  the  outer 
edge  of  the  penumbra  at  d, — t lie  second  contact  with  the 
penumbra.  Since  the  earth  is  so  much  larger  than 


ECLIPSES.  163 

the  moon,  the  eclipse  can  never  be  annular ,  as, 
however,  the  eclipse  may  occur  a  little  above  or  be- 
low the  node,  the  moon  may  only  partly  enter  the 
earth's  shadow,  either  on  its  upper  or  lower  limb. 
From  the  first  to  last  contact  with  the  penumbra, 
five  hours  and  a  half  may  elapse.  Total  eclipses  of 
the  moon  are  rarer  events  than  those  of  the  sun, 
since  the  lunar  ecliptic  limit  is  only  about  12° ;  yet 
they  are  more  frequently  seen  by  us,  (1)  because  each 
one  is  visible  over  the  entire  unillumined  hemisphere 
of  the  earth,  and  also  (2)  because  by  the  diurnal  ro- 
tation during  the  long  duration  of  the  eclipse,  large 
areas  may  be  brought  within  its  limits.  So  it  will 
happen  that  while  the  inhabitants  of  one  district  wit- 
ness the  eclipse  throughout  its  continuance,  those  of 
other  regions  merely  see  its  beginning,  and  others 
only  its  termination.  The  moon  does  not  completely 
disappear  even  in  total  eclipses.  The  cause  of 
this  fact  lies  in  the  refraction  of  the  solar  rays  in 
traversing  the  lower  strata  of  the  earth's  atmos- 
phere ;  they  are  analyzed,  and  purple  our  moon  with 
the  tints  of  sunset.  The  amount  of  refraction  and 
the  color  depend  upon  the  state  of  the  air  at  the 
time. 

HISTORICAL  ACCOUNTS  OF  ECLIPSES. — The  earliest 
account  of  an  eclipse  on  record  is  in  the  Chinese 
annals ;  it  is  thought  to  be  the  solar  eclipse  of  Octo- 
ber 13,  2127  B.  c.  On  May  28,  584  B.  c.,  one  oc- 
curred which  was  predicted  by  Thales,  as  wo  have 
before  mentioned.  In  the  writings  of  the  early  Eng- 


164  THE   SOLAK  SYSTEM. 

lish  chroniclers  are  numerous  passages  relating  to 
eclipses.  William  of  Malmesbury  thus  refers  to  that 
of  August  2,  1133,  which  was  considered  a  presage 
of  calamity  to  Henry  I. :  "  The  elements  manifested 
their  sorrows  at  this  great  man's  last  departure. 
For  the  sun  on  that  day,  at  the  6th  hour,  shrouded 
his  glorious  face,  as  the  poets  say,  in  hideous 
darkness,  agitating  the  hearts  of  men  by  an  eclipse ; 
and  on  the  6th  day  of  the  week,  early  in  the  morn- 
ing, there  was  so  great  an  earthquake,  that  the 
ground  appeared  absolutely  to  sink  down  ;  an  horrid 
noise  being  first  heard  beneath  the  surface."  The 
same  writer,  speaking  of  the  total  eclipse  of  March 
20,  1140,  says :  "  During  this  year,  in  Lent,  on  the 
13th  of  the  kalends  of  April,  at  the  9th  hour  of  the 
4th  day  of  the  week,  there  was  an  eclipse,  through- 
out England,  as  I  have  heard.  With  us,  indeed,  and 
with  all  our  neighbours,  the  obscuration  of  the  Sun 
also  was  so  remarkable,  that  persons  sitting  at  table, 
as  it  then  happened  almost  every  where,  for  it  was 
Lent,  at  first  feared  that  Chaos  was  come  again : 
afterwards  learning  the  cause,  they  went  out  and 
beheld  the  stars  around  the  Sun.  It  was  thought 
and  said  by  many,  not  untruly,  that  the  king  [Ste- 
phen] would  not  continue  a  year  in  the  govern- 
ment." Columbus  made  use  of  an  eclipse  of  the 
moon,  which  took  place  March  1, 1504,  to  relieve  his 
fleet,  which  was  in  great  distress  from  want  of  sup- 
plies. As  a  punishment  to  the  islanders  of  Jamaica, 
who  refused  to  assist  him,  he  threatened  to  deprive 


THE  TIDES.  165 

them  of  the  light  of  the  moon.  At  first  they  were 
indifferent  to  his  threats,  but  "  when  the  eclipse  ac- 
tually commenced,  the  barbarians  vied  with  eacli 
other  in  the  production  of  the  necessary  supplies  for 
the  Spanish  fleet." 

THE  TIDES. 

DESCKIPTION. — Twice  a  day,  at  intervals  of  about 
twelve  hours  and  twenty-five  minutes,  the  water  be- 
gins to  set  in  from  the  ocean,  beating  the  pebbles 
and  the  foot  of  the  rocky  shore,  and  dashing  its 
spray  high  in  air.  For  about  six  hours  it  climbs 
far  up  on  the  beach,  flooding  the  low  lands  and 
transforming  simple  creeks  into  respectable  rivers. 
The  instant  of  high-water  or  flood-tide  being  reached, 
it  begins  to  descend,  and  the  ebb  succeeds  the  flow. 
The  water,  however,  falls  somewhat  slower  than  it 
rose. 

CAUSE  OF  THE  TIDES. — The  tides  are  caused  by  a 
great  wave,  which,  raised  by  the  moon's  attraction, 

Fte.  53. 


Spring  Tidts 


SPKINO  TIDE. 

follows  her  in  her  course  around  the  earth.  The 
sun,  also,  aids  somewhat  in  producing  this  effect; 
but  as  the  moon  is  400  tim^s  nearer  the  earth,  her 


1S6  THE  SOLAR  SYSTEM. 

influence  is  far  greater.  As  the  waters  are  free  to 
yield  to  the  attraction  of  the  moon,  she  draws  them 
away  from  C  and  D  and  they  become  heaped  up  at 
A.  The  earth,  being  nearer  the  moon  than  the 
waters  on  the  opposite  side,  is  more  strongly  at- 
tracted, and  so,  being  drawn  away  from  them,  they 
are  left  heaped  up  at  B.  As  the  result,  high-water 
is  produced  at  A  by  the  water  being  pulled  from  the 
earth,  and  at  B  by  the  earth  being  pulled  from  the 
water.  The  influence  of  the  moon  is  not  instanta- 
neous, but  requires  a  little  time  to  produce  its  full 
effect ;  hence  high- water  does  not  occur  at  any  place 
when  the  moon  is  on  the  meridian,  but  a  few  hours 
after.  As  the  moon  rises  about  fifty  minutes  later 
each  day,  there  is  a  corresponding  difference  in  the 
time  of  high-water.  While,  however,  the  lunar  tide- 
wave  thus  lags  about  fifty  minutes  every  day,  the 
solar  tide  occurs  uniformly  at  the  same  time.  They 
therefore  steadily  separate  from  each  other.  At  one 
time  they  coincide,  and  high-water  is  the  sum  of 
lunar  and  solar  tides ;  at  other  times,  high-water  of 
the  solar  tide  and  low-water  of  the  lunar  tide  occur 
simultaneously,  and  high-water  is  the  difference 
between  the  lunar  and  solar  tides. 

We  should  bear  in  mind  tha  philosophical  truth, 
that  the  tide  in  the  open  sea  ioes  not  consist  of  a 
progressive  movement  of  the  water  itself,  but  only 
of  the  form  of  the  wave. 

Causes  that  modify  the  tides. — At  new  and  full  moon 
(the  syzygies)  the  sun  acts  with  the  moon  (as  in  Fig. 


THE   TIDES.  167 

53)  in  elevating  the  waters ;  this  produces  the  highest 
or  Spring  tide.  In  quadrature  (as  in  Fig.  54),  the 
sun  tends  to  diminish  the  height  of  the  water  :  this  is 
called  Neap-tide.  When  the  moon  is  in  perigee  her 
attraction  is  stronger ;  hence  the  flood-tide  is  higher 
and  the  ebb-tide  lower  than  at  other  times.  This  re- 
Fig.  54. 


Bcap  Tides 


NEAP-TIDE. 


mark  applies  also  to  the  sun.  The  height  of  the  tide 
also  varies  with  the  declination  of  the  sun  and  moon, 
— the  highest  or  equinoctial  tides  taking  place  at  the 
equinoxes,  if,  when  the  sun  is  over  the  equator,  the 
moon  also  happens  to  be  very  near  it :  the  lowest 
occur  at  the  solstices.  The  force  and  direction  of 
the  winds,  the  shape  of  the  coast,  and  the  depth  of 
the  sea  wonderfully  complicate  the  explanation  of 
local  tides. 

Height  of  the  tide  at  different  places. — In  the  open 
sea  the  tide  is  hardly  noticeable,  the  water  some- 
times rising  not  higher  than  a  foot ;  but  where  tho 
wave  breaks  on  the  shore,  or  is  forced  up  into  bays 
or  narrow  channels,  it  is  very  conspicuous.  The 
difference  between  ebb  and  flood  neap-tide  at  New 
York  is  over  three  feet,  and  that  of  spring  tide  over 


168  THE   SOLAR   SYSTEM. 

fivo  feet ;  while  at  Boston  it  is  nearly  double  this 
amount.  A  headland  jutting  out  into  the  ocean  will 
diminish  the  tide  ;  as,  for  instance,  off  Cape  Florida, 
where  the  average  height  is  only  one  and  a  half  feet. 
A  deep  bay  opening  up  into  the  land  like  a  funnel, 
will  converge  the  wave,  as  at  the  Bay  of  Fundy, 
where  it  rolls  in,  a  great  roaring  wall  of  water  sixty 
feet  high,  frequently  overtaking  and  sweeping  off 
men  and  animals.  The  tide  sets  up  against  the 
current  of  rivers,  and  often  entirely  changes  their 
character ;  for  example,  the  Avon  at  Bristol  is  a 
mere  shallow  ditch,  but  at  flood-tide  it  becomes  a 
deep  channel  navigable  by  the  largest  Indiarnen. 

Differential  effect. — The  whole  attraction  of  the 
moon  is  only  T  J-g-  that  of  the  sun :  yet  her  influence  in 
producing  the  tides  and  precession  is  greater,  because 
that  depends  not  upon  the  entire  attraction  either 
exerts,  but  upon  the  difference  between  their  attrac- 
tion upon  the  earth's  centre  and  upon  the  earth's 
nearest  surface.  For  the  moon,  on  account  of  her 
nearness,  the  proportion  of  the  distance  of  these 
parts  is  treble  that  of  the  sun,  and  hence  her  greater 
effect. 

MARS. 

The  god  of  war.    Sign,  $  ,  shield  and  spear. 

DESCRIPTION. — Passing  outward  in  our  survey  of  the 
solar  system,  we  next  meet  with  Mars.  This  is  the 
first  of  the  superior  planets,  and  the  one  most  like 
the  earth.  It  appears  to  the  naked  eye  as  a  bright 


MAES.  169 

red  star,  rarely  scintillating,  and  shining  with  a 
steady  light,  which  distinguishes  it  from  the  fixed 
stars.  Its  ruddy  appearance  has  led  to  its  being 
celebrated  among  all  nations.  The  Jews  gave  it  the 
appellation  of  "  blazing,"  and  it  bore  in  other  lan- 
guages a  similar  name.  At  conjunction  its  apparent 

Fi<r.  53. 


DIAMETER   OP   MARS   AT   EXTREME,    LEAST,   AND   MEAN   DISTANCES. 

diameter  is  only  about  4";  but  once  in  two  years  it 
comes  into  opposition  with  the  sun,  when  its  diam- 
eter increases  to  30".  At  intervals  of  Syr.  7 mo. 
this  occurs  when  the  planet  is  also  in  perihelion 
and  perigee.  Mars  then  shines  with  a  brilliancy 
rivalling  that  of  Jupiter  himself. 

MOTION  IN  SPACE. — Mars  revolves  about  the  Sun 
at  a  mean  distance  of  about  140,000,000  miles.  Its 
orbit  is  sufficiently  flattened  to  bring  it  at  perihelion 
26,000,000  miles  nearer  that  luminary  than  when  in 
aphelion.  Its  motion  varies  in  different  portions  of 
its  orbit,  but  the  average  velocity  is  about  fifteen 

8 


170  THE  SOLAR  SYSTEM. 

miles  per  second.  The  Martial  day  is  about  40  min, 
longer  than  ours,  and  the  year  contains  about  668 
Martial  days,  equal  to  687  terrestrial  days  (nearly 
two  years). 

DISTANCE  FROM  EARTH.— When  in  opposition,  the 
distance  of  Mars  is  (like  that  of  all  the  superior 
planets)  the  difference  between  the  distance  of  the 
planet  and  that  of  the  earth  from  the  Sun :  at  con- 
junction it  is  the  sum  of  these  distances.  If  the 
orbits  were  circular,  these  distances  would  be  the 
same  at  every  revolution.  The  elliptical  figure,  how- 
ever, occasions  much  variation.  Thus,  if  it  is  in 
perihelion  while  the  earth  is  in  aphelion,  the  dis- 
tance is  126,000,000  -  93,000,000  =  33,000,000  miles. 

DIMENSIONS. — Its  diameter  is  a  little  less  than 
5,000  miles.  Its  volume  is  about  J  that  of  the  earth, 
but  as  its  density  is  only  J,  it  follows  that  its  mass 
is  only  £  of  the  terrestrial  mass.  A  stone  let  fall  on 
its  surface  would  fall  not  quite  five  feet  the  first 
second.  It  is  somewhat  flattened  at  the  poles,  and 
bulges  at  the  equator  like  our  globe. 

SEASONS. — The  light  and  heat  of  the  sun  at  Mars 
are  less  than  one  half  that  which  we  enjoy.  Its  axis 
is  inclined  about  28.7°,  therefore  its  zones  and  sea- 
sons do  not  differ  materially  from  our  own  :  its  days, 
also,  as  we  have  seen,  are  of  nearly  the  same  length 
Since,  however,  its  year  is  equal  to  neaily  two  of 
our  years,  the  seasons  are  lengthened  in  proportion. 
There  must  be  a  considerable  difference  between  the 
temperature  of  its  northern  and  southern  hemi- 


MAES.  171 

spheres,  as  the  former  has  its  summer  when  26,000,000 
miles  further  from  the  sun  than  the  latter :  an  in- 
creased length  of  76  days  may,  however,  be  suffi- 
cient compensation.  It  has  an  atmosphere  like  our 
own,  loaded  with  clouds.  Mars  has*  &o  moon.  Its 
nights,  therefore,  are  dark.  Our  own  earth  and 
moon  must  present  in  its  evening  sky  a  very  beauti- 
ful pair  of  planets,  showing  all  the  phases  which 
Mercury  and  Yenus  present  to  us,  the  two  always 
remaining  within  one  half  the  moon's  apparent  di- 
ameter of  each  other. 

TELESCOPIC  FEATURES. — Under  the  telescope,  Mars 
exhibits  slight  phases,  but  by  no  means  to  the  same 

Pig.  56. 


7TSW  OF  XARS. 


extent  as  the  inferior  planets.  Its  surface  appears 
covered  with  dusky  patches,  which  are  believed  to 
be  continents :  these  are  of  a  dull  red  hue.  Other 


17 '2  THE  SOLAR  SYSTEM. 

portions,  of  a  greenish  tint,  are  considered  to  be 
bodies  of  water.  The  proportion  of  land  to  water 
on  the  earth  is  reversed  in  Mars.  "  Here  every  con- 
tinent is  an  island ;  there  every  sea  is  a  lake :  but 
these,  like  our  own  continents,  are  chiefly  confined  to 
one  hemisphere,  so  that  the  habitable  area  of  the 
two  globes  may  not  differ  so  much  as  the  size  of  the 
planets."  The  ruddy  color  of  the  planet  is  thought 
by  Herschel  to  be  due  to  an  ochrey  tinge  in  the 
soil ;  by  others  it  is  attributed  to  peculiarities  of  the 
atmosphere  and  clouds.  Lambert  suggests  that  it 
is  the  color  of  the  vegetation,  which,  on  Mars,  may 
be  red  instead  of  green.  There  are  constant 
changes  going  on  in  the  brightness  of  the  disk, 
owing,  it  is  supposed,  to  the  variation  of  the  clouds 
of  vapor  in  its  atmosphere.  No  mountains  have  yet 
been  discovered.  In  the  vicinity  of  the  poles  are 
brilliant  white  spots,  which  are  considered  to  be 
masses  of  snow.  The  "  snow  zones"  apparently  melt 
and  recede  with  the  return  of  summer  in  each  hemi- 
sphere, and  increase  on  the  approach  of  winter.  "We 
can  thus  from  the  earth  watch  the  formation  of  polar 
ice  and  the  fall  of  snow — in  fact,  all  the  vicissitudes 
of  the  seasons  on  the  surface  of  a  neighboring 
planet. 

THE  MINOK  PLANETS. 

i 

DISCOVERY. — Beyond  Mars  there  is  a  wide  interval 
which  until  the  present  century  was  not  filled.  The 
bold,  imaginative  Kepler  conjectured  that  there  was 


THE  MINOR  PLANETS. 


173 


a  planet  in  this  space.  This  supposition  was  cor- 
roborated by  Titius's  discovery  of  what  has  since 
been  known  as  Bode's  law. 

Take  the  numbers  0,  3,  6,  12,  24,  48,  96,  192,  384, 
each  of  which,  after  the  second,  is  double  the  pre- 
ceding one.  If  we  add  4  to  each  of  these  numbers, 
we  form  a  new  series  : 

4,  7,  10,  16,  28,  52,  100,  196,  388. 

At  the  time  this  law  was  discovered,  these  numbers 
represented  very  nearly  the  proportionate  distance 
from  the  sun  of  the  planets  then  known,  taking  the 
earth's  distance  as  ten,  except  that  there  was  a  blank 
opposite  28.*  This  naturally  led  to  inquiry,  and  a 
systematic  effort  to  solve  the  mystery.  On  the  1st 
day  of  January,  1801,  the  nineteenth  century  was 
inaugurated  by  Piazzi's  discovery  of  the  small 
planet  Ceres,  at  almost  the  exact  distance  necessary 
to  fill  the  gap  in  Bode's  series.  This  was  soon  fol- 
lowed by  the  announcement  of  other  new  planets, 
until  (1870)  there  are  one  hundred  and  twelve,  and  a 
probability  of  many  more.  Indeed,  Leverrier  has 
calculated  that  there  may  be  perhaps  150,000  in  all 


*  PIQUETS. 

True  dis- 
tance 
from  •. 

Distance 
by  Bode's 
law. 

PLANETS. 

True  dis- 
tance 
from  •. 

Distance 
by  Bode'a 
law. 

Vulcan  

Ceres  

27  C6 

28  00 

Mercury  
Venus  

8.87 
7.23 

4.00 
7.00 

Jupiter  
Saturn  

62.03 
95.39 

52.00 
10000 

Earth  .... 

10.00 

10.00 

Uranus  .  . 

191  82 

19600 

Mara     

1523 

1600 

Neptune 

30087 

38800 

174  THE  SOLAR  SYSTEM. 

DESCRIPTION. — These  minor  worlds,  or  "  pocket 
planets,"  as  Herschel  styled  them,  are  extremely 
diminutive.  The  largest  of  them  is  Pallas,  whose 
diameter  is  perhaps  600  miles.  Those  recently  dis- 
covered are  so  small  that  it  is  difficult  to  decide 
which  is  the  smallest.  A  French  astronomer  recently 
remarked  concerning  them,  that  a  "good  walker 
could  easily  make  the  tour  of  one  in  a  day;"  a 
prairie  farmer  would  need  to  pre-empt  a  whole  one 
for  a  flourishing  cornfield.  They  all  revolve  about 
the  sun  in  regular  orbits,  comprising  a  zone  about 
100,000,000  miles  in  width.  Their  paths  are  va- 
riously inclined  to  the  ecliptic ;  Massilia's  41',  while 
that  of  Pallas  rises  34°. 

ORIGIN. — One  theory  concerning  the  origin  of  these 
small  planets  is,  that  they  are  the  fragments  of  a 
large  planet  which,  in  a  remote  antiquity,  has  been 
shivered  to  pieces  by  some  terrible  catastrophe. 
"One  fact  seems  above  all  others  to  confirm  the 
idea  of  an  intimate  relation  between  these  planets. 
It  is  this:  if  their  orbits  consisted  of  solid  rings, 
they  would  be  found  so  entangled  that  it  would  be 
possible,  by  taking  up  any  one  at  random,  to  lift 
all  the  rest."  Another  theory  is  given  under  the 
"  Nebular  Hypothesis." 

Names  and  signs. — Ceres,  thjp  first  discovered,  re- 
ceived the  symbol  9 ,  a  sickle.  This  was  appropri- 
ate, since  that  goddess  was  supposed  to  preside  over 
harvests.  Pallas,  the  second,  named  from  the  god- 
dess of  wisdom  and  scientific  warfare,  obtained  the 


JTJPITEB.  175 

sign  4 ,  the  head  of  a  spear.  To  Juno,  the  third 
planet,  was  assigned  o ,  a  sceptre  surmounted  with 
a  star,  the  emblem  of  the  queen  of  heaven.  An 
altar  with  fire  upon  it,  fi ,  appropriately  represented 
Vesta,  the  household  goddess,  whose  sacred  fire  was 
kept  burning  continually.  In  this  way  names  of 
goddesses  and  appropriate  symbols  were  used  to 
designate  the  minor  planets  which  were  earliest  dis- 
covered. Since  then  a  simple  circle  with  the  num- 
ber inclosed  has  been  adopted;  thus  (D  represents 
Ceres — (D  is  the  sign  of  Pallas. 


JUPITEE. 

The  king  of  the  gods.    Sign  y. ,  a  hieroglyphic  representation  of  an  eagle 
"the  bird  of  Jove." 

DESCRIPTION. — From  the  smallest  members  of  the 
solar  system  we  now  pass  at  once  to  the  largest 
planet — the  colossal  Jupiter.  Its  peculiar  splendor 
and  brilliancy  distinguish  it  from  the  fixed  stars, 
and  vie  even  with  the  lustre  of  Yenus.  It  is  one  of 
the  five  planets  discovered  in  primitive  ages.  In 
those  early  times,  Jupiter  was  supposed  to  be  the 
cause  of  storm  and  tempest.  Pliny  thought  that 
lightning  owed  its  origin  to  this  planet.  An  old  al- 
manac of  1368,  foretelling  the  harmless  condition  of 
Jupiter  for  a  certain  month,  says,  "  Jubit  es  hote 
and  moyste  and  does  weel  til  al  thynges  and  noyes 
nothing.*' 


176  THE  SOLAR  SYSTEM. 

MOTION  IN  SPACE. — Jupiter  revolves  about  the  sun 
at  a  mean  distance  of  475,000,000  miles.  His  orbit 
has  much  less  eccentricity  than  those  of  the  smaller 
planets.  Were  his  path  very  elliptical,  the  attrac- 
tion of  the  sun  would  be  insufficient  to  bring  him 
back  from  its  extreme  limit,  and  the  huge  un- 
wieldy planet  would  plunge  headlong  into  space. 
This  careful  fitting,  whereby  the  plan  is  always 
modified  to  accomplish  an  end,  is  everywhere 
characteristic  of  nature,  and  is  a  continued  rev- 
elation of  its  common  Author.  The  revolution 
of  Jupiter  among  the  fixed  stars  is  slow  and  ma- 
jestic, comporting  well  with  his  vast  dimensions 
and  the  dignity  conferred  by  four  attendant  worlds. 
He  advances  through  the  zodiac  at  the  rate  of  one 
constellation  yearly ;  so  that  if  we  locate  the  planet 
now,  a  year  hence  we  can  find  it  equally  advanced 
in  the  next  sign.  Yet  slowly  as  he  seems  to  travel 
through  the  heavens,  he  is  bowling  along  through 
space  at  the  enormous  speed  of  500  miles  per  min- 
ute. The  Jovian  day  is  only  equal  to  about  ten  of 
our  hours,  while  his  year  is  lengthened  to  about 
12  of  our  years,  comprising  near  10,000  of  his  days. 

DISTANCE  FROM  EARTH. — Once  in  thirteen  months 
Jupiter  is  in  opposition,  and  his  distance  from  the 
earth  is  measured  by  the  difference  of  the  distances 
of  the  two  bodies  from  the  sun.  At  the  expira- 
tion of  half  this  time  he  is  in  conjunction,  and  his 
distance  from  us  is  measured  by  the  sum  of  these 
distances. 


JUPITER. 


177 


Fipr.  57. 


DIMENSIONS. — Its  diameter  is  about  88,000  miles, 
or  one-tenth  of  the  sun.  Its  volume  is  1,400  times 
that  of  the  earth, 
and  much  exceeds 
th  at  of  all  the  other 
planets  combined. 
Seen  at  the  dis- 
tance of  the  moon, 
this  immense 
globe  would  em- 
brace 1,200  times 
the  space  of  the 
full  moon.  Jupi- 
ter's density  is 
only  one-fifth  that 

of  the  earth ;  moreover,  its  rapid  rotation  upon  its 
axis,  whereby  a  particle  on  the  equator  revolves 
with  a  velocity  of  467  miles  per  minute  against  the 
earth's  17  miles  per  minute,  must  produce  a  power- 
ful centrifugal  force  which  materially  diminishes  the 
weight  of  all  objects  near  its  equator.  Consequently 
a  stone  let  fall  on  Jupiter  would  pass  through  but 
about  thirty-nine  feet  the  first  second.  As  a  result 
of  this  rapid  rotation,  the  planet  is  one  of  the  most 
flattened  of  any  in  the  solar  system — the  equatorial 
diameter  exceeding  the  polar  by  about  5,000  miles. 

SEASONS. — As  the  axis  of  Jupiter  is  but  slightly 
inclined  from  a  perpendicular  to  the  plane  of  its 
orbit,  there  is  but  little  difference  in  the  length  of 
its  days  and  nights,  which  are  each  of  about  five 

8* 


178  THE  SOLAR  SYSTEM, 

hours'  duration.  At  the  poles  the  sun  is  visible  foi 
nearly  six  years,  and  then  remains  set  for  the  same 
length  of  time.  The  seasons  also  are  but  slightly 
varied.  Summer  reigns  near  the  equator,  while  the 
temperate  regions  enjoy  perpetual  spring.  The  light 
and  heat  of  the  sun  are  only  -fa  of  that  which  we  re- 
ceive; yet  peculiarities  of  soil  or  atmosphere  may 
compensate  this  difference.  The  evening  sky  on 
Jupiter  must  be  inexpressibly  magnificent ;  besides 
the  glittering  stars  which  adorn  our  heavens,  four 
moons,  waxing  and  waning,  each  with  its  diverse 
phase,  illuminate  its  night.  All  the  starry  exhibition 
sweeps  through  the  sky  in  five  hours. 

TELESCOPIC  FEATURES. — Jupiter's  moons. — Under 
the  telescope  Jupiter  presents  a  beautiful  Copernican 
system  in  miniature.  Four  small  stars — moons — are 
seen  to  accompany  it  in  its  twelve-yearly  revolutions. 
From  hour  to  hour  their  positions  vary,  and  they 
seem  to  oscillate  from  one  side  to  the  other  of  the 
planet.  At  one  time  there  will  be  two  on  each  side, 
and  again,  three  on  one  side ;  while  the  remaining 
star  is  left  alone.  They  are  also  frequently  found 
to  disoppear,  one,  two,  or  even  three  at  a  time,  and, 
more  rarely,  all  four  at  once.  There  are  well- 
authenticated  instances  on  record  of  their  having 
been  seen  by  the  naked  eye.  Among  others,  the 
following  singular  case  is  mentioned.  Wrangle,  the 
celebrated  Eussian  traveller,  states,  that  when  in  Si- 
beria, he  once  met  a  hunter,  who  said,  pointing  to 
Jupiter,  "  I  have  just  seen  that  star  swallow  a  small 


JUPITER. 


179 


one  and  then  vomit  it  up  again."  These  moons  are 
called  by  the  ordinal  numbers,  reckoning  outward 
from  the  planet.  With  an  ordinary  glass,  there  is 
nothing  to  distinguish  them  from  small  stars.  The 
Hid,  however,  being  the  largest  and  brightest,  will 
generally  be  identified  easiest.  The  1st  satellite  ap- 
pears to  the  inhabitants  of  the  planet  almost  as 
large  as  our  moon  to  us ;  the  lid  and  Hid  about 
half  as  large.  Their  real  size  and  density  are  in- 
dicated in  the  following  table.  It  will  be  seen  that 
the  IVth  is  about  the  weight  of  cork,  and  the  1st 
and  lid  are  still  lighter. 

SATELLITES  OF  JUPITER. 


Mean  distance 
from  Jupiter. 

Diameter. 

Density. 
Water  as  1. 

Sidereal  period. 

I  lo 

267380 

2,352  m. 

.114 

D.      H.       M. 

1    18    28 

II.  Europa  

425,156 

2,099  " 

.171 

3    13      4 

HI.  Ganymede  
IV.  Callisto......... 

678,393 
1,192,823 

3,436  " 
2,929  " 

.396 
.222 

7      3    43 
19    16    32 

;t  is  no^iceablfe-that  here  are  four  satellites  revolv- 
ing 'about  Jupiter,  one  of  them  larger  than  the  planet 
Mercury,  and  each  far  surpassing  in  size  the  minor 
planets  between  Mars  and  Jupiter.  The  moons  are 
not  only  thus  distinguished  by  their  various  dimen- 
sions, but  also  by  the  variety  of  their  color.  The 
1st  and  lid  have  a  bluish  tint,  the  Hid  a  yellow, 
and  the  IVth  a  reddish  shade.  The  total  space  oc- 
cupied by  this  miniature  system  is  about  two  and 
a  half  million  miles  in  diameter. 

Eclipse  of  the  moons. — Jupiter,  like  allcelestialbodies 
not  self-luminous,  casts  into  space  a  cone  of  shade. 


180 


THE   SOLAR  SYSTEM. 


The  1st,  lid,  and  nid  satellites  revolve  in  or- 
bits but  very  little  inclined  to  the  plane  of  the 
planet's  orbit.  During  each  revolution  they  pass 

Fig.  58. 


ECLIPSES  AJTO  OCCTTLTA.TION8  OF  JUPITEB  8  MOONS. 

between  the  Sun  and  Jupiter,  producing  a  solai 
eclipse ;  and  also  by  passing  through  the  shadow  of 


JUPITER.  181 

the  planet  itself,  cause  to  themselves  an  eclipse  of 
the  sun,  and  to  Jupiter  an  eclipse  of  a  moon.  The 
IVth  passes  through  a  path  more  inclined,  and  there- 
fore its  eclipses  are  less  frequent :  instead  of  being 
fully  eclipsed,  it  sometimes  just  grazes  the  shadow, 
as  it  were,  and  so  its  light  is  much  diminished. 
Through  a  telescope  we  can  distinctly  watch  the 
disappearance  or  immersion  of  the  satellites  in  the 
planet's  shadow,  their  reappearance  or  emersion,  and 
also  their  transits,  as  a  round  black  dot  or  shadow 
moving  across  the  disk  of  Jupiter.  In  the  cut,  we 
see  represented  the  various  positions  of  the  moons  : 
the  1st  is  eclipsed;  the  lid  is  passing  across  the 
disk  of  the  planet  on  which  its  shadow  is  also  thrown ; 
the  IIEd  is  just  behind  the  planet,  and  so  occulted  or 
concealed,  while  it  has  not  yet  entered  the  shadow; 
the  IVth  is  in  view  from  the  earth.  These  satellites 
revolve  with  great  rapidity,  as  is  necessary  in  order 
to  overcome  the  superior  attraction  of  the  planet  and 
prevent  being  drawn  to  its  surface.  The  1st  goes 
through  all  its  phases  in  1|  days,  and  the  lYth  in  less 
than  twenty  days.  A  spectator  on  Jupiter  might 
witness,  during  the  Jovian  year,  4,500  eclipses  of 
the  moon  (moons),  and  about  the  same  number  of 
the  sun. 

Jupiter's  lelts. — These  are  dusky  streaks  of 
varying  breadth  and  number,  lying  more  or  less 
parallel  to  the  planet's  equator,  but  terminating  at  a 
short  distance  from  the  edges  of  the  disk.  Between 
these  a  brighter,  often  rose-colored  space,  marks  the 


182  THE  SOLAR  SYSTEM. 

equatorial  regions.  They  are  not  permanent,  but 
change  sometimes  very  materially  in  the  course  of 
a  few  minutes.  Occasionally  only  two  or  three 
broad  belts  are  seen ;  at  other  times  a  dozen  narrow 
ones  appear.  It  is  supposed  that  the  planet  is  en- 
veloped in  dense  masses  of  cloud,  and  that  the  belts 
are  merely  fissures,  laying  bare  the  solid  body  be- 
neath. The  parallel  appearance  is  doubtless  due  to 
strong  equatorial  currents,  analogous  to  our  trade- 
winds. 

VELOCITY  OF  LIGHT. — By  an  attentive  examination 
of  the  eclipses  of  Jupiter's  moons,  Homer  (a  Danish 
astronomer,  in  1617)  was  led  to  discover  the  pro- 
gressive motion  of  light.  Before  him,  it  had  been 
considered  instantaneous.  He  noticed  that  the  ob- 
served times  of  the  eclipses  were  sometimes  earlier 
and  sometimes  later  than  the  calculated  times,  ac- 
cording as  Jupiter  was  nearest  or  furthest  from  the 
earth.  His  investigations  convinced  him  that  it 
requires  about  16 \  min.  for  light  to  traverse  the  orbit 
of  the  earth.  Bomer's  conclusion  has  since  been 
verified  by  the  phenomena  of  aberration  of  light. 
The  velocity  of  light  is  about  183,000  miles  pel 
second.  (See  14  Weeks  in  Philosophy,  p.  189.) 

SATUEN. 

The  god  of  time.    Sign  * ,  an  ancient  ecythe. 

DESCRIPTION. — We  now  reach,  in  our  outward  jour- 
ney from  the  sun,  the  most  remote  world  known  to 
the  ancients.  On  account  of  its  distance,  it  shines 


SATURN. 


183 


with  a  feeble  but  steady  pale  yellow  light,  which  dis- 
tinguishes it  from  the  fixed  stars.  Its  orbit  is  so 
vast  that  its  movement  among  the  constellations 
may  be  easily  traced  through  one's  lifetime.  It  re- 
quires two  and  a  half  years  to  pass  through  a  single 
sign  of  the  zodiac ;  hence,  when  once  known,  it  may 
be  easily  found  again.  The  earth  leaves  it  at  con- 
7  junction,  makes  a  yearly  revolution  about  the  sun, 
comes  to  its  starting  point,  and  overtakes  Saturn  in 
about  thirteen  days  thereafter.*  On  account  of  its 
slow,  dreary  pace,  Saturn  was  chosen  by  the  ancients 
as  the  symbol  for  lead.  It  is  smaller  than  Jupiter, 
but  much  more  gorgeously  attended.  Besides  a 
retinue  of  eight  satellites,  it  is  surrounded  by  a  sys- 
tem of  rings,  some  shining  with  a  golden  light  and 
others  transparent — a  spectacle  which  is  as  wonder- 
ful as  it  is  unique. 

MOTION  IN 
SPACE.—  Saturn 
revolves  about 
the  sun  at  a 
mean  distance 
of  872,000,000 
miles.  The 
eccentricity  of 
its  orbit  is  a 
trifle  more  than 
that  of  Jupiter, 


*  From  this  the  year  of  Saturn  may  be  determined.  As  13  :  378 
days   :  •   Earth's  year  :   Saturn's  year  =  30  yr.  nearly 


184  THE   SOLAR   SYSTEM. 

so  that  while  it  may  at  perihelion  come  fifty  mil- 
lion miles  nearer  than  its  mean  distance,  at  aphe- 
lion it  swings  off  as  much  beyond.  We  can  form 
some  estimate  of  the  size  of  its  immense  orbit, 
when  we  remember  that  it  is  moving  along  at  the 
rate  of  21,000  miles  per  hour,  and  yet  as  we  look 
at  it  from  night  to  night,  we  can  scarcely  detect  any 
change  of  place.  The  Saturnian  year  is  equal  to 
about  thirty  of  ours,  and  comprises  nearly  25,000 
Saturnian  days,  each  of  which  is  about  ten  and  a 
half  hours  in  length. 

DISTANCE  FROM  EARTH. — This  is  found  in  the  same 
manner  as  that  of  the  other  superior  planets,  being 
least  in  opposition  and  greatest  at  conjunction.  As 
the  earth  and  Saturn  occupy  different  portions  of 
their  orbits,  the  distances  between  them  at  different 
times  may  vary  200,000,000  miles. 

DIMENSIONS. — Its  diameter  is  about  72,000  miles. 
Its  volume  is  nearly  750  times  that  of  the  earth.  Its 
density  is  very  low  indeed,  being  much  less  than  that 
of  water,  and  about  the  same  as  that  of  pine  wood. 
The  Saturnian  force  of  gravity  is  therefore  scarcely 
greater  than  the  terrestrial,  so  that  a  stone  falls 
toward  the  surface  of  that  immense  globe  only  about 
seventeen  feet  the  first  second. 

SEASONS. — The  light  and  heat  of  the  sun  at  Saturn 
are  only  j^-  that  which  we  receive.  The  axis  of 
Saturn  is  inclined  from  a  perpendicular  to  the 
plane  of  its  orbit  about  31°.  The  seasons  there- 
fore are  similar  to  those  on  the  earth,  but  on  a 


SATURN.  185 

larger  scale.  The  sun  climbs  in  summer  about  8° 
higher  above  the  horizon,  and  sinks  correspondingly 
lower  in  winter.  The  tropics  are  16°  further  apart, 
and  the  arctic  and  antarctic  circles  8°  further  from 
the  poles.  Each  of  Saturn's  seasons  lasts  more  than 
seven  of  our  years.  There  is  about  fifteen  years 
interval  between  the  autumn  and  spring  equinoxes, 
and  between  the  summer  and  winter  solstices.  For 
fifteen  years  the  sun  shines  on  the  north  pole,  and  a 
night  of  the  same  length  envelops  the  south  pole. 
The  atmosphere  is  doubtless  very  dense,  as  the  belts 
would  seem  to  indicate. 

TELESCOPIC  FEATURES.  —  Saturn's  Rings.  Galileo 
first  noticed  something  peculiar  in  the  shape  of  Sat- 
urn. Through  his  imperfect  telescope  it  seemed  to 
have  on  each  side  a  small  planet  like  a  supporter, 
to  help  old  Saturn  on  his  way.  He  therefore  an- 
nounced to  his  friend  Kepler  his  curious  discovery, 
that  "Saturn  is  threefold."  As  the  planet,  how- 
ever, approached  its  equinoxes,  these  attendants  van- 
ished altogether  from  his  simple  instrument.  This 
was  a  great  perplexity  to  Galileo,  and  he  never 
solved  the  mystery.  When  the  rings  were  after- 
ward seen,  their  real  form  was  not  known.  They 
were  supposed  to  be  a  kind  of  handle  attached  to  the 
planet,  but  for  what  purpose  was  not  explained. 

The  series  consists  of  three  rings  of  unequal 
oreadth,  surrounding  the  planet  at  the  equator.  The 
exterior  ring  is  separated  from  the  middle  one  by  a 
distinct  break,  while  the  interior  one  seems  joined 


186  THE  SOLAR  SYSTEM. 

fco  the  middle  one.  They  differ  in  their  brightness 
the  exterior  ring  is  of  a  grayish  tint ;  the  middle  one 
is  the  most  brilliant  and  is  more  luminous  than  Sat- 
urn itself ;  the  interior  is  dusky  and  has  a  purple 
tinge.  The  exterior  and  middle  rings  are  both 
opaque  and  cast  on  the  planet  a  distinct  shadow ; 
while  the  interior  one  is  so  transparent  that  it  ap- 
pears upon  the  globe  of  Saturn  as  a  dark  band 
through  which  the  surface  of  the  planet  is  readily 
seen.  The  dimensions  of  the  rings  are  given  in  the 
following  table  (Guillemin) : 

Miles. 

Diameter  of  exterior  ring 173,500 

Breadth  of  exteriorring 10,000 

Diameter  of  middle  ring 150,000 

Breadth  of  middle  ring 18,300 

Distance  between  exterior  and  middle  ring 1,750 

Diameter  of  interior  ring 113,400 

Breadth  of  interiorring 9,000 

Distance  of  interior  ring  from  planet 10,150 

Entire  breadth  of  ring  system 39,050 

Thickness  of  rings  not  more  than 100 

The  rings  revolve  around  Saturn  in  about  10£ 
hours,  in  the  same  direction  as  the  planet  revolves 
on  its  axis.  The  globe  of  Saturn  is  not  exactly  at 
the  centre  of  the  rings.  This  fact,  combined  with 
the  rotary  motion,  is  essential  to  the  stability  of  the 
rings,  preventing  them  from  being  precipitated  in 
an  overwhelming  ruin  and  devastation  upon  the 
body  of  the  planet. 

Phases  of  the  rings. — The  plane  of  the  rings  is  in- 
clined 28°  to  the  ecliptic.  In  its  revolution  about 
the  sun,  the  axis  of  Saturn  remaining  parallel  to 


SATURN. 


187 


itself,  the  sun  sometimes  illumines  the  northern 
and  sometimes  the  southern  face  of  the  rings.  At 
Saturn's  equinoxes  the  edge  only  receives  the  light, 
and  the  rings  are  invisible  to  us,  except  with  the 


Fig.  60. 


PHASES  OF  SATURN'S  KINGS. 

most  powerful  telescopes,  and  then  only  as  a  line  of 
light.  The  body  of  the  planet  constantly  cuts  off 
the  sun's  rays  from  a  portion  of  the  rings,  and  also 
serves  to  conceal  from  our  view  some  of  the  lumin- 
ous part.  By  a  careful  study  of  the  cut  these  vari- 
ous positions  of  the  planet  and  rings,  with  the  most 
favorable  times  for  observation,  may  be  understood. 
Belts. — The  surface  of  Saturn  is  traversed  by  dusky 
belts  of  a  less  distinct  and  definite  appearance  than 


188  THE  SOLAR  SYSTEM. 

those   upon  Jupiter.      The   equatorial  regions   are 
brighter  than  the  other  parts  of  the  disk ;  the  poles 
especially  are  less  luminous. 
SATELLITES. — Saturn  has  eight  satellites,  named— 

1.  Mimas.  3.  Tethys.       5.  Rhea.       7.  Hyperion. 

2.  Enceladus.        4  Dione.        6.  Titan.       8.  lapetus. 

lapetus  is  the  largest  of  these,  and  in  size  exceeds 
Mars.  Enceladus  and  Mimas  are  the  faintest  of 
twinklers,  and  can  only  be  seen  with  a  powerful 
telescope,  and  under  most  favorable  circumstances. 
They  were  first  detected  by  Herschel,  "threading 
like  pearls  the  silver  line  of  light,"  to  which  the 
ring,  then  seen  edgewise,  was  reduced, — advancing 
off  it  at  either  end,  returning,  and  then  hiding  them- 
selves behind  the  planet.  The  first  four  of  these 
moons  are  nearer  to  Saturn  than  our  moon  to  the 
earth,  but  lapetus  is  nearly  ten  times  as  distant :  so 
that  the  diameter  of  the  Saturnian  system  is  nearly 
four  and  a  half  million  miles.  The  movements  are 
extremely  rapid.  Mimas  traverses  a  space  equal  to 
the  diameter  of  our  moon  in  two  minutes,  passing 
from  new  to  full  in  twelve  hours, — a  little  more  than 
a  Saturnian  day. 

SATURNIAN  SCENERY. — The  grandeur  and  magnifi- 
cence of  the  scenery  upon  Saturn  undoubtedly  far 
surpass  anything  with  which  we  are  familiar.  In 
the  cut  is  given  an  ideal  view  of  a  landscape  located 
upon  the  planet  at  a  latitude  of  about  28°,  taken 
about  midnight.  The  rings  form  an  immense  arch, 


URANUS. 


189 


which   spans   the   sky   and    sheds   a   soft  radiance 
around;  while  to  add  to  the  strange  beauty  of  the 


Fig.  61. 


IDEAL  LANDSCAPE  ON  SATURN. 


Saturnian  night,  eight  moons  in  all  their  different 
phases,  full,  new,  crescent,  or  gibbous,  light  up  the 
starry  vault. 

UKANUS. 

"  Heaven,"  the  most  ancient  of  the  gods.    Sign  JJl ;  H,  the  initial  letter  of 
Herschel,  with  a  planet  suspended  from  the  cross-bar. 

DESCRIPTION. — On  the  13th  of  March,  1781,  between 
10  and  11  P.  M.,  Sir  William  Herschel  was  engaged 
in  examining  with  his  great  telescope  some  stars 
in  the  constellation  Gemini.  One  small  star  at- 
tracted his  attention,  which  he  accordingly  observed 
with  a  higher  magnifying  power,  when,  unlike  the 


190  THE  SOLAB  SYSTEM. 

effect  produced  on  the  fixed  stars,  its  disk  widened, 
Watching  it  for  several  nights,  he  detected  its  mo- 
tion in  space,  and,  mistaking  its  true  character, 
announced  the  discovery  of  a  new  comet.  A  few 
months'  examination  revealed  the  error,  and  the  new 
body  was  universally  admitted  to  be  a  member  of 
the  solar  system — new  to  us,  but  older  perhaps  than 
our  own  world.  It  is  now  known  that  Uranus  had 
been  previously  observed  by  other  astronomers. 
Indeed,  Le  Monier  at  Paris  had  watched  it  for 
twelve  successive  nights,  but  pronounced  it  a  fixed 
star.  Since  he  had  also  seen  it  on  previous  occa- 
sions, had  he  been  an  orderly  observer,  he  would 
doubtless  have  detected  its  planetary  character ;  but 
he  was  extremely  careless,  as  may  be  inferred  from 
the  fact  related  by  Arago,  that  he  had  been  shown 
one  of  Le  Monier's  observations  of  this  planet  writ- 
ten on  a  paper  bag  which  originally  contained  hair- 
powder  purchased  at  a  perfumer's.  Uranus  may  be 
seen  by  a  person  of  strong  eyesight  in  a  perfectly 
dark  sky,  if  he  previously  knows  its  exact  position 
among  the  stars.  Its  faintness  is  due  to  its  great 
distance  from  the  earth.  Were  it  as  near  as  the  sun, 
it  would  appear  twice  as  large  as  Jupiter. 

MOTION  IN  SPACE. — Uranus  revolves  about  the  sun 
at  a  mean  distance  of  1,754,000,000  miles.  Its  year 
exceeds  eighty-four  of  ours. 

DIMENSIONS. — Its  diameter  is  about  33,000  miles. 
It  is  lighter  than  water,  having  a  density  about 
equal  to  that  of  ice. 


NEPTUNE.  191 

SEASONS. — We  know  little  of  the  seasons  of  Uranus. 
Since  its  axis  lies  in  the  plane  of  its  orbit,  the  sun 
winds  in  a  spiral  form  around  the  whole  planet.  The 
light  and  heat  are  only  y^Vtr  of  that  which  we 
receive ;  the  light  is  about  the  quantity  which  would 
be  afforded  by  three  hundred  full  moons.  The  in- 
habitants of  Uranus  can  see  Saturn,  and  perhaps 
Jupiter,  but  none  of  the  planets  within  the  orbit 
of  the  latter. 

TELESCOPIC  FEATURES. — No  spots  or  belts  have 
been  discovered  with  any  telescope  yet  made.  The 
time  of  rotation  and  other  features  so  familiar  to  us 
in  the  nearer  planets,  are  unknown  with  regard  to 
Uranus. 

Satellites. — Uranus  has  four  moons,  of  which 
little  is  known  except  the  curious  fact  that  their 
orbits  are  nearly  perpendicular  to  the  plane  of  the 
planet's  orbit,  and  that  their  movements  are  retro- 
grade— i.  e.,  in  the  same  direction  as  the  hands  of  a 
watch. 

NEPTUNE. 

The  god  of  the  sea.    Sign  j ,  his  trident. 

DESCRIPTION. — Neptune  is  the  far-off  sentinel  at 
the  very  outposts  of  the  solar  system,  being  the  most 
distant  planet  of  which  we  have  any  knowledge.     It 
is  invisible  to  the  naked  eye,  and  appears  in  the  tel 
oscope  as  a  star  of  the  eighth  magnitude. 

DISCOVERY. — For  many  years  the  motions  of  Ura- 
nus were  such  as  to  baffle  the  most  perfect  calcula- 


192  THE  SOLAR  SYSTEM. 

tions.  While  far-distant  Saturn  came  around  to  his 
place  true  to  the  minute  and  second,  even  after  his 
journey  of  nearly  thirty  years,  Uranus  defied  arith- 
metic, and  refused  to  conform  to  the  time  set  down 
for  him  on  the  heavenly  dial. 

At  length  it  was  suggested  by  several  astronomers 
that  there  was  another  planet  outside  of  its  orbit, 
whose  attraction  produced  these  perturbations.  So 
marked  was  this  impression  with  Herschel,  that  he 
writes  :  "  "We  see  it  as  Columbus  saw  America  from 
the  shores  of  Spain.  Its  movements  have  been  felt 
trembling  along  the  far-reaching  line  of  our  analysis 
with  a  certainty  not  far  inferior  to  ocular  demonstra- 
tion." Finally,  two  young  mathematicians,  Lever- 
rier  of  Paris,  and  Adams  of  Cambridge,  England, 
each  unknown  to  the  other,  set  themselves  about  the 
task  of  finding  the  place  of  this  new  planet.  The 
problem  was  this :  Given  the  disturbances  produced 
by  the  attraction  of  the  unknown  planet,  to  find  its  orbit 
and  its  place  in  the  orbit.  Adams,  after  assiduous 
labor  for  nearly  two  years,  completed  his  calcula- 
tions and  submitted  them  to  Prof.  Airy,  the  Astron- 
omer Koyal,  in  October,  1845.  In  the  summer  of 
1846,  Leverrier  laid  a  paper  before  the  Academy  of 
Sciences  in  Paris,  announcing  the  position  of  the 
unknown  planet.  Prof.  Airy,  hearing  of  this,  was  so 
impressed  with  the  value  of  Adams's  calculations, 
that  he  wrote  to  Prof.  Challis,  of  Cambridge,  to  use 
his  large  telescope  to  search  that  quarter  of  the 
heavens.  Prof.  Challis  did  as  requested,  and  saw  a 


NEPTUNE.  193 

star  which  afterward  proved  to  be  the  planet  so 
anxiously  sought  for,  although  at  that  time  he  failed 
to  ascertain  its  true  character.  On  September  23d, 
of  the  same  year,  Leverrier  wrote  to  Berlin,  asking 
for  assistance  in  searching  for  the  planet.  Dr.  Galle, 
that  same  evening,  turned  the  large  telescope  of  the 
Observatory  to  the  place  indicated,  and  almost  im- 
mediately detected  a  bright  star  not  laid  down  in 
the  maps.  This  proved  to  be  the  predicted  planet, 
found  within  less  than  a  degree  of  the  spot  de- 
scribed by  Leverrier.  Such  is  the  history  of  one  of 
the  grandest  achievements  of  the  human  mind.  It 
stands  as  an  ever  fresh  and  assuring  proof  of  the 
exactness  of  astronomical  calculations,  and  the  pow- 
er of  the  intellect  to  understand  the  laws  of  the  God 
of  Nature. 

MOTION  IN  SPACE. — Neptune  revolves  about  the 
sun  at  a  mean  distance  of  about  2,750,000,000  of 
miles.  The  Neptunian  year  is  equal  to  nearly  165 
terrestrial  ones.  Its  motion  in  its  orbit  is  the  slow- 
est of  any  of  the  planets,  since  it  is  the  most  remote 
from  the  sun.  The  velocity  decreases  from  Mercury, 
which  moves  at  the  rate  of  105,000  miles  per  hour, 
to  Neptune,  whose  rate  is  only  12,000  miles. 

DIMENSIONS. — Its  diameter  is  about  37,000  miles. 
Its  volume  is  nearly  100  times  that  of  the  earth.  Its 
density  is  about  that  of  Uranus,  a  little  less  than  that 
of  water. 

SEASONS. — As  the  inclination  of  its  axis  is  un- 
known, nothing  can  be  ascertained  concerning  its 

9 


194  THE  SOLAR  SYSTEM. 

seasons.  The  sun  gives  to  Neptune  but  y^Vfr  the 
light  and  heat  which  we  receive. 

Though  at  the  extreme  of  the  solar  system,  2,650 
millions  of  miles  beyond  us,  the  same  heavens  bend 
above,  the  same  starry  sky  is  seen  by  night — the 
Milky  Way  is  no  nearer  to  the  eye,  the  fixed  stars 
shine  no  more  brightly.  The  planets,  however,  are 
all  too  near  the  sun  to  be  seen,  except  Saturn  and 
Uranus.  The  Neptunian  astronomers,  if  there  be 
any,  are  well  situated  for  observing  the  orbits  of 
correts,  and  for  measuring  the  annual  parallax  of 
the  stars,  since  they  have  an  orbit  of  5,500  million 
miles  in  diameter,  and  hence  the  angle  must  be  30 
times  as  great  as  that  which  the  terrestrial  orbit 
affords. 

TELESCOPIC  FEATURES. — On  account  of  the  recent- 
ness  of  the  discovery  of  this  planet  and  its  immense 
distance,  nothing  is  known  of  its  rotation  or  physical 
features. 

Satellites. — Neptune  has  one  moon,  at  nearly  the 
same  distance  from  it  as  our  own  moon  is  from  the 
earth.  The  revolution  of  this  about  the  planet, 
which  is  accomplished  in  about  six  days,  has  fur- 
nished the  materials  for  calculating  the  mass  of 
Neptune. 

METEOKS  AND  SHOOTING  STAES. 

DESCRIPTION. — All  are  familiar  with  those  lumin- 
ous bodies  that  flash  through  our  atmosphere  as  if 


METEORS  AND   SHOOTING   STARS. 


195 


the  stars  were  indeed  falling  from  heaven.  Differ- 
ent names  have  been  applied  to  them,  although  the 
distinction  is  not  very  definite.  (1)  Aerolites  are  those 


A   METEOR  WITH  ITS  TBAIN. 


stony  masses  which  fall  to  the  earth.     (2)  Shooting 
Stars  are  those  evanescent  brilliant  points  that  snd- 


196  THE   SOLAR  SYSTEM. 

denly  dart  through  the  higher  regions  of  the  air, 
leaving  a  fiery  train  behind.  (3)  Meteors  are  lumin- 
ous bodies  which  have  a  sensible  diameter  and  a 
spherical  form.  They  frequently  pass  over  a  great 
extent  of  country,  and  are  seen  for  some  seconds  of 
time.  Many  leave  behind  a  train  of  glowing  sparks ; 
others  explode  with  reports  like  the  discharge  of 
artillery, — the  pieces  either  continuing  their  course, 
or  falling  to  the  earth  as  aerolites.  Some  meteors, 
doubtless,  after  having  favored  us  with  a  transient 
illumination,  pass  on  into  space ;  some  are  vapor- 
ized; while  others  are  burned  and  the  ashes  and 
fragments  fall  to  the  ground. 

AEROLITES. — The  fall  of  aerolites  is  frequently  men- 
tioned and  well  authenticated.  Chinese  records  tell 
of  one  as  long  ago  as  in  616  B.  c.,  which,  in  its  fall, 
broke  several  chariots  and  killed  ten  men.  A  block 
of  stone,  equal  to  a  full  wagon-load,  fell  in  the  Helles- 
pont, B.  c.  465.  By  the  ancients,  these  stones  were 
held  in  great  repute.  The  Emperor  Jehangire,  it  is 
related,  had  a  sword  forged  from  a  mass  of  meteoric 
iron  which  fell  in  the  Punjab  in  1620.  In  1795,  a 
mass  was  seen,  by  a  ploughman,  to  descend  toward 
the  earth  at  a  spot  not  far  from  where  he  was  stand- 
ing. It  threw  up  the  soil  on  every  side,  and  pene- 
trated some  distance  into  the  solid  rock  beneath, 
In  1807,  a  shower  of  stones,  one  weighing  200  Ibs., 
fell  at  "Weston,  Connecticut.  These  aerolites  are 
sometimes  seen  to  plunge  downward  into  the  earth, 
aiuj  are  found  while  yet  glowing.  A  mass  thus  fell  in 


METEORS  AND  SHOOTING  STABS.  197 

South  America,  which  was  estimated  to  weigh  fifteen 
tons.  When  first  discovered,  it  was  so  hot  as  to 
prevent  all  approach.  Upon  its  cooling,  many  efforts 
were  made,  by  some  travellers  who  were  present,  to 
detach  specimens,  but  its  hardness  was  too  great  for 
any  tools  which  they  possessed.  There  is  a  mass  of 
meteoric  iron  in  Yale  College  cabinet,  weighing 
1,635  Ibs. 

Aerolites  consist  of  elements  which  are  familiar. 
The  analysis  of  these  stellar  masses  gives  us  names 
as  commonplace  as  if  they  had  known  a  far 
less  romantic  origin — oxygen,  sulphur,  phosphorus, 
iron,  tin,  copper :  in  all,  nineteen  elements  have 
been  found.  This  fact  is  interesting  as  reveal- 
ing something  of  the  chemistry  of  the  region  of 
space,  concerning  which  we  otherwise  know  nothing. 
The  compounds,  however,  are  very  peculiar,  so  as 
to  distinguish  an  aerolite  from  any  terrestrial  sub- 
stance. For  example,  meteoric  iron,  a  prominent 
constituent  of  aerolites,  is  an  alloy  that  has  never 
been  found  in  terrestrial  minerals. 

METEORS. — The  records  of  meteors  are  still  more 
wonderful.  It  is  related  that  at  Crema,  Italy,  one 
day  in  the  15th  century,  the  sky  at  noonday  be- 
came dark, — a  cloud  of  appalling  blackness  over- 
spreading the  heavens.  Upon  this  cloud  appeared 
the  semblance  of  a  great  peacock  of  fire  flying  over 
the  town.  This  suddenly  changed  to  a  huge  pyramid, 
that  rapidly  traversed  the  sky.  Thence  arose  awful 
lightnings  and  thunderings,  amid  which  there  feD 


198  THE   SOLAR   SYSTEM. 

upon  the  plain  great  rocks,  some  of  which  weighed 
100  Ibs.  In  1803  a  brilliant  fireball  (meteor)  was 
seen  traversing  Normandy  with  great  velocity,  and 
some  moments  after,  frightful  explosions,  like  the 
noise  of  cannon  or  roll  of  musketry,  were  heard  com- 
ing from  a  single  black  cloud  hanging  in  a  clear 
sky;  they  were  prolonged  for  five  or  six  minutes. 
These  discharges  were  followed  by  a  great  shower 
of  stones,  some  weighing  over  24  Ibs.  In  1819  a 
meteor  was  witnessed  in  Massachusetts  and  Mary- 
land, the  diameter  of  which  was  estimated  at  half 
a  mile.  Its  height  was  thought  to  be  about  25  miles. 
In  July,  1860,  a  brilliant  fireball  passed  over  the 
state  of  New  York  from  west  to  east,  and  was  last 
seen  far  out  at  sea. 

SHOOTING  STARS. — One  of  the  earliest  accounts  of 
star-showers  is  that  which  relates  how,  in  472,  the 
sky  at  Constantinople  appeared  to  be  alive  with  fly- 
ing stars  and  meteors.  In  some  Eastern  annals  we 
are  told  that  in  October,  1202,  "  the  stars  appeared 
like  waves  upon  the  sky.  They  flew  about  like 
grasshoppers,  and  were  dispersed  from  left  to  right." 
It  is  recorded  that  in  the  time  of  King  William  II. 
there  occurred  in  England  a  wonderful  shower  of 
stars,  which  "  seemed  to  fall  like  rain  from  heaven. 
Aai  eye-witness  seeing  where  an  aerolite  fell,  cast 
water  upon  it,  which  was  raised  in  steam  with  a 
great  noise  of  boiling."  Kastel  says  concerning  it : 
"  By  the  report  of  the  common  people  in  this  kynge's 


METEORS  AND  SHOOTING  STABS.  199 

time,  diverse  great  wonders  were  seene,  and  there- 
fore the  kynge  was  told  by  diverse  of  his  familiars, 
that  God  was  not  content  with  his  lyvyng." 

In  more  modern  times,  the  most  remarkable  ac- 
counts are  those  of  the  showers  of  November  12th, 
1799,  and  1833.  Humboldt,  in  describing  the  former, 
says  the  sky  was  covered  with  innumerable  fiery 
trails,  which  incessantly  traversed  the  sky  from 
north  to  south.  From  the  beginning  of  the  phenom- 
enon there  was  not  a  space  in  the  heavens  three 
times  the  diameter  of  the  moon  which  was  not  filled 
every  instant  with  the  celestial  fireworks, — large 
meteors  blending  constantly  their  dazzling  brilliancy 
with  the  long  phosphorescent  paths  of  the  shooting 
stars.  Tto  latter  shower  was  most  brilliant  on  this 
continent,  and  was  visible  from  the  lakes  to  the  equa- 
tor. The  scene  was  one  of  the  most  imposing  grand- 
eur. Phosphoric  lines  swept  over  the  sky  like  the 
flakes  of  a  sharp  snow-storm.  Large  meteors  darted 
across  the  heavens,  leaving  luminous  trains  behind 
them  that  were  visible  sometimes  for  half  an  hour  : 
they  generally  shed  a  soft  white  light ;  occasionally, 
however,  yellow,  green,  and  other  colors  varied 
the  scene.  Irregular  fireballs,  almost  stationary, 
glared  in  the  sky;  one  especially,  larger  than  the 
moon,  hung  in  mid  air  over  Niagara  Falls  and' 
mingled  its  ghastly  light  with  the  foam  and  mist  of 
the  cataract.  The  shower  commenced  near  mid- 
night, but  was  at  its  height  about  5  A.M.  In  many 


200  THE  SOLAR  SYSTEM. 

sections  of  the  country,  the  people  were  terror- 
stricken  by  the  awful  spectacle,  and  supposed  that 
the  end  of  the  world  had  come. 

An  inferior  shower  was  seen  in  1831  and  1832 ; 
and  so  also  in  the  succeeding  years,  until  1839. 
These  did  not  compare  in  brilliancy  with  the  re- 
markable phenomenon  of  1833. 

There  was  an  interval  of  about  33  or  34  years 
between  the  great  showers  of  1799  and  1833 ;  this 
seemed  to  indicate  another  shower  in  November, 
1866.  The  people  of  both  hemispheres  were  liter- 
ally awake  to  the  subject.  Newspapers  aroused  the 
most  sluggish  imagination  with  thrilling  accounts  of 
the  scenes  presented  in  1799  and  1833.  Extempore 
observatories  were  founded  in  every  convenient  point. 
Watchmen  were  stationed,  and  the  city  bells  were  to 
be  rung  on  the  appearance  of  the  first  wandering 
celestial  visitor.  The  exact  night  was  not  definitely 
known,  but  for  fear  of  a  mistake,  the  llth,  12th,  and 
13th  were  generally  observed.  All  painfully  testify 
to  those  nights  being  clear  and  beautiful  as  moon- 
light and  starlight  could  make  them.  The  anxious 
vigils,  the  fruitless  scannings  of  the  sky,  the  disap- 
pointment, the  meteors  that  were  dimly  tJiought  to 
be  seen — all  these  are  recorded  in  the  memory  of 
the  temporary  astronomers  of  that  year.  While, 
however,  the  people  of  America  were  thus  disap- 
pointed, there  was  being  enacted  in  England  a  dis- 
play brilliant  indeed,  though  inferior  to  the  one  of 


METEORS  AND  SHOOTING  STAES.  201 

1833.  The  staff  at  Greenwich  Observatory  counted 
about  8,000  meteors ;  other  observers,  however,  made 
a  much  lower  estimate.  Chambers,  in  describing  the 
phenomena,  says :  "  Of  the  large  number  of  descrip- 
tions which  came  under  my  eye  in  manuscript  and 
in  print,  the  following  is  a  fair  example  :  'From  11^ 
p.  M.  until  2  A.  M.  we  were  much  interested  in  watch- 
ing the  shooting  stars ;  anything  so  beautiful  I  never 
saw,  especially  about  one  o'clock,  when  they  were 
most  brilliant ;'  and  so  on  by  the  ream."  In  Novem- 
ber, 1867,  the  long-expected  shower  was  seen  in  this 
country,  but  it  failed  to  satisfy  the  public  expecta- 
tion. The  sky  was,  however,  illumined  with  shoot- 
ing stars  and  meteors,  some  of  which  exceeded  even 
Jupiter  or  Yenus  in  brilliancy. 

Number  of  meteors  and  shooting  stars. — In  a  paper 
lately  read  by  Prof.  Newton,  it  is  estimated  that  the 
average  number  of  meteors  that  traverse  the  atmos- 
phere daily,  and  which  are  large  enough  to  be  visi- 
ble to  the  eye  on  a  dark  clear  night,  is  7,500,000 ; 
and  if  to  these  the  telescopic  meteors  be  added,  the 
number  would  be  increased  to  400,000,000.  In  the 
space  traversed  by  the  earth  there  are,  on  the  aver- 
age, in  each  volume  the  size  of  our  globe  (including 
its  atmosphere),  as  many  as  13,000  small  bodies, 
each  one  capable  of  furnishing  a  shooting  star  visi- 
ble under  favorable  circumstances  to  the  naked  eye. 

Annual  periodicity  of  the  star-showers. — On  almost 
any  clear  night,  from  five  to  seven  shooting  stars 


202  THE   SOLAR  SYSTEM. 

may  be  seen  per  hour,  but  in  certain  months  they 
are  much  more  abundant.  Arago  names  the  fol- 
lowing principal  dates : 

April  4-11 ;  17-25.         October  (about)  15. 
August  9-11.  November  11-13. 

ORIGIN. — Aerolites,  meteors,  and  falling  stars  all 
seem  to  have  a  common  origin.  They  are  produced 
by  small  bodies — planets  in  miniature — which  are 
revolving,  like  our  earth,  about  the  sun.  Their  or- 
bits intersect  the  orbit  of  the  earth,  and  if  at  any 
time  they  reach  the  point  of  crossing  exactly  with 
the  earth,  there  is  a  collision.  Their  mass  is  so 
small,  that  the  earth  is  not  jarred  any  more  than 
is  a  railway  train  by  a  pebble  thrown  against  it. 

These  small  bodies  may  come  near  the  earth  and 
be  drawn  to  its  surface  by  the  power  of  attraction  ; 
or  they  may  simply  sweep  through  the  higher  re- 
gions of  the  atmosphere,  and  there  escape  its  gr&sp ; 
or,  finally,  they  may,  under  certain  conditions,  be 
compelled  to  revolve  many  times  around  the  earth 
as  satellites.  Indeed,  a  French  astronomer  esti- 
mates that  there  is  one  now  circling  about  the 
earth  at  a  distance  of  5,000  miles.  This  companion 
of  our  moon  has  a  period  of  three  hours  and  twenty 
minutes.  The  average  velocity  of  these  meteoric 
bodies  or  bolides,  as  they  are  frequently  called,  is 
thirty-six  miles  per  second — much  greater  than  that 
of  Mercury  itself.  As  they  sweep  through  the  air, 


METEORS  AND  SHOOTING  STARS.  203 

the  friction  partly  arrests  their  motion,  and  converts 
it  into  heat  and  light.  The  body  thus  becomes  visi- 
ble to  us.  Its  size  and  direction  determine  its  ap- 
pearance. If  very  small,  it  is  consumed  in  the  upper 
regions,  and  leaves  only  the  luminous  trail  of  a  shoot- 
ing star.  If  of  large  size,  it  may  sweep  along  at  a 
high  elevation,  or  plunge  directly  toward  the  ground. 
Becoming  highly  heated  in  its  course,  it  sheds  a 
vivid  light,  while,  unequally  expanding,  it  explodes, 
throwing  off  large  fragments  which  fall  to  the  earth 
as  aerolites,  or  continue  their  separate  course  as 
meteors.  The  cinders  of  the  portion  consumed  rain 
down  on  us  as  fine  meteoric  dust. 

METEORIC  KINGS. — These  little  bodies,  it  is  thought, 
do  not  generally  revolve  individually  about  the  sun, 
but  myriads  of  them  are  collected  in  several  rings, 
and  when  the  earth  passes  through  one  of  these 
floating  girdles,  a  star-shower  follows.  This  would 
account  for  their  regular  appearance  in  certain  sea- 
sons of  the  year.  In  the  cut  we  see  how  one  ring, 
intersecting  the  earth's  orbit  at  two  points,  would 
account  for  the  August  and  November  showers. 
Another  ring,  more  inclined  to  the  earth's  path,  and 
crossing  it  nearer  the  aphelion  point,  would  produce 
the  April  showers. 

Recent  investigators  are  inclined  to  the  view  that 
there  are  separate  rings  for  each  of  the  established 
periods,  and  that  they  are  very  elliptical.  The  No- 
vember ring  seems  to  have  its  perihelion  near  the 


204  THE  SOLAR  SYSTEM. 

ecliptic,  and  its  aphelion  beyond  the  orbit  of  Uranus; 
while  the  August  ring  extends  beyond  the  solar  sys- 
tem. The  day  of  the  month  in  which  the  great  No- 
vember shower  occurs  is  becoming  later  at  each  re- 
Fig.  63. 


METEORIC  RING. 


turn  ;  hence  it  is  believed  that  the  nodes  of  that  ring 
are  slowly  travelling  eastward  along  the  ecliptic.  The 
meteoric  bodies  are  supposed  to  be  quite  uniformly 
distributed  through  the  August  stream,  but  very  un- 


METEORS  AND   SHOOTING   STARS.  205 

equally  thiough  the  November  one.  On  this  ac- 
count, the  former  star-showers  are  quite  regular, 
while  the  latter  vary  in  brilliancy  through  periods 
of  33^  years. 

RELATION  BETWEEN  METEORS  AND  COMETS. — The 
orbit  of  the  November  shower  is  found  to  be  almost 
identical  with  that  of  the  comet  of  1866 ;  while  the 
August  stream  is  in  the  track  of  the  comet  of  1862. 
It  is  a  popular  theory  that  these  comets  are  only 
clusters  of  meteors  crowded  so  closely  together  as  to 
be  visible  by  the  reflected  light  of  the  sun.  The  single 
meteors  are  too  small  to  be  seen,  except  when  they 
plunge  into  the  earth's  atmosphere  and  take  fire. 
On  the  other  hand,  Herschel  thinks  that  meteors  are 
the  dissipated  parts  of  comets  torn  into  shreds  by 
the  sun's  attraction. 

RADIANT  POINT. — A  star  (jx)  in  the  blade  of  the 
sickle  is  the  point  from  which  the  stars  in  the  Novem- 
ber shower  seem  to  radiate,  while  one  in  Perseus  (7) 
is  the  radiant  point  of  the  August  shower.  In  the 
shower  of  1866,  two  observers,  who  counted  the 
falling  stars  at  the  rate  of  2,500  per  hour,  saw  only 
five  whose  paths,  if  traced  back,  would  not  meet 
in  Leo. 

METEOROLOGICAL  EFFECT. — The  temperature  of 
August  and  November  is  said  to  be  considerably  in- 
creased by  this  ring  of  meteoric  bodies,  which  pre- 
vents the  heat  of  the  earth  from  radiating  into 
space.  A  corresponding  decrease  of  temperature 
in  February  and  May  is  caused  by  the  stream 


206  THE  SOLAB  SYSTEM. 

• 

or  ring  of  meteors  coming  between  the  sun  and 
earth. 

HEIGHT. — Herschel  estimates  the  average  height 
of  shooting  stars  above  the  earth  at  73  miles  at  their 
appearance  and  52  at  their  disappearance. 

WEIGHT. — Prof.  Harkness  estimates  that  the  aver- 
age weight  of  shooting  stars  does  not  differ  much 
from  one  grain. 

COMETS. 

We  come  now  to  notice  a  class  of  bodies  the 
most  fascinating,  perhaps,  of  any  in  astronomy. 
The  suddenness  with  which  comets  flame  out  in 
the  sky,  the  enormous  dimensions  of  their  fiery 
trains,  the  swiftness  of  their  flight,  the  strange  and 
mysterious  forms  they  assume,  their  departure  as 
unheralded  as  their  advent — all  seem  to  bid  defiance 
to  law,  and  partake  only  of  the  marvellous.  Su- 
perstitious fears  have  always  been  excited  by  their 
appearance,  and  they  have  been  looked  upon  in 
every  age  as 

"  Threatening  the  world  with  famine,  plague,  and  war ; 
To  princes,  death ;  to  kingdoms,  many  corses ; 
To  all  estates,  inevitable  losses ; 
To  herdsmen,  rot ;  to  ploughmen,  hapless  seasons ; 
To  sailors,  storms ;  to  cities,  civil  treasons." 

Thus  the  comet  of  43  B.C., which  appeared  just 
after  the  assassination  of  Julius  Csesar,  was  looked 
upon  by  the  Komans  as  a  celestial  chariot  sent  to 
convey  his  soul  heavenward.  An  old  English  writer 


COMETS.  207 

observes  :  "  Cometes  signifie  corruptions  of  the  ayre. 
They  are  signs  of  earthquakes,  of  warres,  of  chang- 
yng  kyngedomes,  great  dearthe  of  corn,  yea,  a  com- 
mon death  of  man  and  beast."  Another  remarks : 
"Experience  is  an  eminent  evidence  that  a  comet, 
like  a  sword,  portendeth  war ;  and  a  hairy  comet,  or  a 
comet  with  a  beard,  denoteth  the  death  of  kings,  as 
if  God  and  nature  intended  by  comets  to  ring  the 
knells  of  princes,  esteeming  bells  in  churches  upon 
earth  not  sacred  enough  for  such  illustrious  and  emi- 
nent performances." 

DESCRIPTION. — The  term  comet  signifies  a  hairy 
body.  A  comet  consists  usually  of  three  parts ; — the 
nucleus,  a  bright  point  in  the  centre  of  the  head, ;  the 

Fig:  64.  Fig.  65. 


COMKT  WITHOUT      A  NUCLEUS.  COMET  WITH  A  NUCLEUS. 

coma  (hair),  the  cloud-like  mass  surrounding  the  nu- 
cleus ;  and  the  tail,  a  luminous  train  extending  gen- 
erally in  a  direction  from  the  sun.  There  are  comets 
without  the  tail,  and  others  with  several,  while  some 
are  deprived  of  even  the  nucleus.  These  last  consist 
merely  of  a  fleecy  mass,  known  to  be  comets  from 


208  THE  SOLAR  SYSTEM. 

their  orbits  and  rapid  motion.  Comets  are  not  con- 
fined, like  the  planets,  to  the  limits  of  the  zodiac, 
but  appear  in  every  quarter  of  the  heavens,  and  move 
in  every  conceivable  direction.  "When  first  seen, 
the  comet  resembles  a  faint  spot  of  light  upon  the 
dark  background  of  the  sky :  as  it  approaches  the 
sun  the  brightness  increases,  and  the  tail  begins  to 
show  itself.  Generally  it  is  brightest  near  perihelion, 
and  gradually  fades  away  as  it  recedes,  until  it  is 
finally  lost,  even  to  the  telescope. 

THE   TIME   OF   THE    GREATEST    BRILLIANCY   depends 

somewhat  on  the  position  of  the  earth.  If,  as  rep- 
resented in  the  figure,  the  earth  is  at  a  when  the 
comet,  moving  toward  perihelion,  is  at  r,  the  comet 
will  appear  more  distinct  than 
when  it  is  more  distant  at  s,  al- 
though at  the  latter  point  it 
is  really  brighter.  If,  how- 
ever, the  earth  is  at  c  or  b  at 
the  time  of  perihelion,  the  com- 
et would  be  much  more  con- 
spicuous. Again,  if  the  earth 
is  passing  from  a  to  "b  during  the  .time  the  comet  is 
near  the  sun,  it  will  appear  less  brilliant  than  if  it 
were  moving  from  c  to  d,  as  we  should  then  be  much 
nearer  it  during  its  greatest  illumination. 

NUMBER  OF  COMETS. — Kepler  remarks  that  there 
are  as  many  "  comets  in  the  heavens  as  fish  in  the 
sea."  Arago  has  estimated  that  there  are  17,500,000 
within  the  solar  system,  basing  his  calculations  on  the 


ORBIT  OF  COMET. 


COMETS.  209 

number  known  to  exist  between  the  sun  and  Mercury. 
Of  this  vast  number,  few  are  visible  to  the  naked 
eve,  and  a  still  less  number  attract  observation,  ow- 
ing to  their  inferior  size  and  brilliancy.  Many  are 
doubtless  lost  to  our  sight  by  being  above  the  hori- 
zon in  the  daytime.  Seneca  mentions  that  during  a 
total  solar  eclipse,  a  large  and  splendid  comet  sud- 
denly made  its  appearance  near  the  sun. 

ORBITS  or  THE  COMETS. — Comets  form  a  part  of 
the  solar  system,  and  are  subject  to  the  laws  of  grav- 
itation. Like  the  planets,  they  revolve  around  the 
sun,  but  they  differ  in  the  form  of  their  orbits. 
While  the  planets  move  in  paths  varying  but  little 
from  circular,  and  thus  never  depart  so  far  from  the 
sun  as  to  be  invisible  to  us,  the  comets  travel  in  ex- 
tremely elongated  (flattened)  ellipses,  so  that  they 
can  be  observed  by  us  only  through  a  very  small 
portion  of  their  paths.  In  Fig.  67  are  represented  the 
three  general  classes  of  their  orbits.  A  comet  travel- 
ling along  an  elliptical  orbit,  though  it  may  pass  far 
from  the  sun,  will  yet  return  within  a  fixed  time; 
one  pursuing  either  a  parabolic  or  hyperbolic  curve 
cannot  return,  as  the  two  sides  separate  from  each 
other  more  and  more.  Many  of  the  comets  of  the 
first  class  have  been  calculated,  and  they  have  re- 
peatedly visited  our  portion  of  the  heavens ;  while 
those  of  the  other  classes,  having  once  formed  part 
of  our  system,  go  away  forever,  seeking  perhaps  in 
the  far-off  space  another  sun,  which  in  turn  they 
will  abandon  as  they  have  our  own. 


210 


THE   SOLAR  SYSTEM. 


Fig.  67. 


THREE  FORMS  OP  COMETARY  OBBITB. 


CALCULATION  OF  A  COMET'S  EETUEN. — As  we  can 
observe  so  small  a  proportion  of  the  entire  orbit,  it 
is  very  difficult,  indeed  oftentimes  impossible,  to 
decide  whether  it  is  an  ellipse,  hyperbola,  or  para- 
bola. A  few  are  known  to  move  in  clearly  ellip- 
tical paths,  and  their  movements  have  been  so 
accurately  estimated  that  it  is  possible  to  predict 
their  exact  place  in  the  starry  vault  on  any  given 


COMETS.  211 

day  and  hour.  The  other  comets  may  never  return, 
or  at  least  not  for  centuries  hence.  They  may  be 
paying  our  sun  their  first  visit ;  or  if  they  have  swept 
through  the  solar  system  before,  it  may  have  been 
at  so  remote  a  time  that  no  record  is  preserved, 
even  if  it  were  not  before  the  creation  of  man.  Un- 
der these  circumstances  it  is  obviously  extremely 
difficult  to  determine  the  times  of  these  apparently 
erratic  wanderers ;  yet,  in  spite  of  all  these  obsta- 
cles, some  have  been  tracked  far  into  space  beyond 
the  telescopic  view.  For  example,  the  comet  of 
1844  is  announced  to  pay  a  visit  to  the  astronomers 
of  the  year  of  our  Lord  101,844.  The  period  of  the 
comet  of  1744,  is  fixed  at  122,683  years. 

DISTANCE  FKOM  THE  SUN. — The  comets  at  their 
perihelion  sweep  very  near  the  sun.  Thus  the  one 
of  1680  came  where  the  temperature  was  estimated 
by  Newton  to  be  about  2,000  times  that  of  red-hot 
iron.  The  nearest  approach  known  is  that  of  the 
comet  of  1843,  whose  perihelion  distance  was  but 
about  30,000  miles  from  the  surface  of  the  sun ;  in 
fact,  it  doubled  around  that  body  in  two  hours'  time. 
(Guillemin.)  The  greatest  aphelion  distance  yet 
estimated  is  that  of  the  comet  of  1844,  which  is 
over  400,000,000,000  miles.  The  velocity  varies,  of 
course,  with  the  position  in  the  orbit.  The  comet  of 
1680  moved  in  perihelion  at  the  rate  of  over  two 
hundred  and  seventy-seven  miles  per  second ;  while 
in  aphelion  its  velocity  is  only  about  six  miles  per 
hour. 


212  THE  SOLAR  SYSTEM. 

DENSITY  OF  COMETS. — The  quantity  of  matter  con- 
tained in  a  comet  is  exceedingly  small.  Telescopic 
stars  even  are  visible  through  them.  The  comet  of 
1770  became  entangled  among  Jupiter's  moons,  and 
remained  there  four  months  without  interfering  with 
their  movements  in  the  least;  indeed,  so  far  from 
that,  its  own  orbit  was  so  much  changed  by  the  prox- 
imity, that  from  a  periodical  return  of  5J  years,  it 
has  not  been  seen  since.  The  same  comet  came 
within  1,400,000  miles  of  the  earth  without  produ- 
cing any  sensible  effect.  In  1861,  we  have  good 
reason  to  suppose  that  the  earth  actually  passed 
through  the  tail  of  a  comet,  its  presence  being 
indicated  only  by  a  peculiar  phosphorescent  mist. 
So  that  even  should  our  earth  run  full-tilt  against 
a  comet,  the  shock  would  be  quite  imperceptible.* 
Still,  however  lightly  we  may  speak  of  the  proba- 
bility of  such  a  collision,  we  must  remember  that 
there  are  comets  of  greater  solidity.  Donati's,  for 
instance,  is  estimated  to  be  about  -fa  the  bulk  of 
the  earth.  The  concussion  of  such  a  body,  moving 

*  "  However  dangerous  might  be  the  shock  of  a  comet,  it  might 
be  so  slight  that  it  would  only  do  damage  at  that  part  of  the  earth 
where  it  actually  struck ;  perhaps  even  we  might  cry  quits,  if, 
while  one  kingdom  were  devastated,  the  rest  of  the  earth  were 
to  enjoy  the  rarities  which  a  body  coming  from  so  far  might 
bring  to  it.  Perhaps  we  should  be  very  surprised  to  find  that  the 
debris  of  these  masses  that  we  despised  were  formed  of  gold  or 
diamonds;  but  who  would  be  the  more  astonished — we  or  the 
comet-dwellers  who  would  be  cast  on  our  earth  ?  What  strange 
beings  each  would  find  the  other !"  Lettre  sur  la  Combte — (M 
De  Maupertuis.) 


COMETS.  213 

with  the  speed  of  a  cannon-ball,  would  undoubtedly 
produce  a  very  sensible  effect. 

It  is  not  understood  whether  comets  shine  by  their 
own  or  by  reflected  light.  If,  however,  their  nuclei 
consist  of  white-hot  matter,  a  passage  through  such 
a  furnace  would  be  any  thing  but  desirable  or  satis- 
factory. After  all  the  calculations  of  Astronomy,  our 
only  safety  lies  in  ttat  Almighty  Power  which  traces 
the  path  and  guides  the  course  alike  of  planets  and 
comets :  He,  whose  eye  marks  the  fall  of  the  spar- 
row, sees  as  well  the  flight  of  the  worlds  He  has 
created. 

VARIATIONS  IN  FORM  AND  DIMENSIONS. — Comets  ap- 
pear to  be  subject  to  constant  variations.  They  are 
now  generally  thought  to  decrease  in  brilliancy  at 
each  successive  revolution  about  the  sun.  The  same 
comet  may  present  itself  sometimes  with  a  tail,  and 
sometimes  without.  When  the  comet  first  appears, 
there  is  generally  no  tail  visible,  and  the  light  is 
faint.  As  it  approaches  the  sun,  however,  its  bright- 
ness increases,  the  tail  shoots  out  from  the  coma, 
and  grows  daily  in  length  and  splendor.  Supernu- 
merary tails,  shorter  and  less  distinct  than  the  prin- 
cipal one,  dart  out,  but  they  generally  soon  disap- 
pear, as  if  from  lack  of  material.  The  tail  of  the 
comet  of  1843,  just  after  the  perihelion,  increased  in 
length  5,000,000  miles  per  day.  As  the  tail  thus 
extended,  the  nucleus  was  correspondingly  con- 
tracted, so  that  this  comet  actually  "  exhausted 
itself  in  the  manufacture  of  its  own  tail." 


214  THE  SOLAR  SYSTEM. 

REMARKABLE  COMETS. — Among  the  many  comets 
celebrated  in  history,  we  shall  only  notice  some  of 
those  that  have  appeared  in  the  present  century. 
The  great  comet  of  1811  was  a  magnificent  spec- 
tacle. The  head  was  112,000  miles  in  diameter ;  the 
nucleus  was  400  miles ;  while  the  tail,  of  a  beautiful 
fan-shape,  stretched  out  112,000,000  miles.  The 
aphelion  distance  of  this  comet  is  fourteen  times 
that  of  Neptune,  or  40,000,000,000  miles.  It  is  an- 
nounced to  return  in  thirty  centuries !  To  what 
profound  depths  of  space,  beyond  the  solar  system, 
beyond  the  reach  of  the  telescope,  must  such  a 
journey  extend ! 

The  comet  of  1835  is  commonly  known  as  Halley 's 
comet.  This  is  remarkable  as  being  the  first  comet 
whose  period  of  revolution  was  satisfactorily  estab- 
lished. Dr.  Halley,  on  examining  the  accounts  of 
the  great  comets  of  1531,  1607,  and  1682,  suspected 
that  they  were  only  the  reappearance  of  the  same 
comet,  whose  period  he  fixed  at  about  75  years.  He 
finally  ventured  to  predict  the  return  of  the  comet 
about  the  end  of  1758  or  beginning  of  1759.  Although 
Halley  did  not  live  to  see  his  prophecy  fulfilled,  great 
interest  was  felt  in  the  result.  It  was  not  destined, 
however,  for  a  professional  astronomer  to  be  the  first 
to  detect  the  comet.  A  peasant  near  Dresden  saw 
it  on  Christmas  night,  1758.  The  history  of  this 
comet,  as  it  has  been  traced  back  by  its  period  of 
seventy-five  years,  is  quite  eventful.  It  was  seen  in 
England  in  1066,  when  it  was  looked  upon  with 


COMETS.  215 

dread  as  the  forerunner  of  the  victory  of  William  of 
Normandy.  It  was  then  equal  to  the  full  moon  in 
size.  In  1456,  its  tail  reached  from  the  horizon  to 
the  zenith.  It  was  supposed  to  indicate  the  success 
of  Mahomet  II.,  who  had  already  taken  Constanti- 
nople, and  threatened  the  whole  Christian  world. 
Pope  Calixtus  III.,  therefore,  ordered  extra  Ave 
Marias  to  be  repeated  by  everybody,  and  also  the 
church  bells  to  be  rung  daily  at  noon  (whence  origi- 
nated the  custom  now  so  universal).  A  prayer  was 
added  as  follows :  "  Lord,  save  us  from  the  devil,  the 
Turk,  and  the  comet."  In  1223,  it  was  considered 
the  precursor  of  the  death  of  Philip  Augustus.  The 
first  recorded  appearance  of  Halley's  comet  was 
B.  c.  130,  when  it  was  supposed  to  herald  the  birth  of 
Mithridates. 

TJie  comet  of  1843  was  so  intensely  brilliant  that  it 
was  visible  in  full  daylight.  It  was  so  near  the 
sun  as  "  almost  to  graze  his  surface." 

Encke's  comet  has  a  period  of  only  3J  years.  A 
most  interesting  discovery  has  been  made  from  ob- 
servations upon  its  motion.  The  comet  returns  each 
time  to  its  perihelion  about  2  J  hours  earlier  than  the 
most  perfect  calculations  indicate.  Hence,  Prof. 
Encke  has  been  led  to  conjecture  that  space  is  filled 
with  a  thin,  ethereal  medium  capable  of  diminishing 
the  centrifugal  force,  and  thus  contracting  the  orbifc 
of  a  comet. 

Donates  comet,  which  appeared  in  1858,  was  the 
subject  of  universal  wonder.  When  first  discovered, 


216  THE  SOLAR  SYSTEM. 

in  June,  it  was  240,000,000  miles  from  the  earth.  In 
August,  traces  of.  a  tail  were  noticed,  which  expanded 
in  October  to  about  50,000,000  miles  in  length.  This 

Fig.  68. 


DONATI'8  COMET. 


comet,  though  small,  lias  never  been  exceeded  in 
the  brilliancy  of  the  nucleus  and  the  graceful  cur- 
vature of  the  tail.  It  will  return  in  about  2,000 
years. 


ZODIACAL  LIGHT. 


217 


ZODIACAL  LJOHT. 


ZODIACAL  LIGHT. 

DESCRIPTION. — If  we  watch  the  western  horizon  in 
March  or  April,  just  after  sunset,  we  shall  sometimes 
see  the  short  twilight  of  that  season  illuminated  by 


10 


218  THE  SOLAR  SYSTEM. 

a  faint,  nebulous  light,  of  a  conical  shape,  flashing 
upward,  often  as  high  as  the  Pleiades.  In  September 
and  October,  at  early  dawn,  the  same  appearance 
can  be  detected  near  the  eastern  horizon.  The 
light  can  be  seen  in  this  latitude  only  on  the  most 
favorable  evenings,  when  the  sky  is  clear  and  the 
moon  absent.  Even  then,  it  will  be  frequently  con- 
founded with  the  Milky  Way  or  auroral  lights.  At 
the  base  it  is  of  a  reddish  hue,  where  it  is  so  bright 
as  very  often  to  efface  the  smaller  stars.  In  tropical 
regions  the  zodiacal  light  is  perpetual,  and  shines 
with  a  brilliancy  sufficient,  says  Humboldt,  to  cast  a 
sensible  glow  on  the  opposite  part  of  the  heavens. 

ORIGIN. — The  commonly  received  opinion  is,  that 
it  is  caused  by  a  faint  cloud-like  ring,  perhaps  a  me- 
teoric zone,  that  surrounds  the  sun,  and  only  be- 
comes visible  to  us  when  the  sun  himself  is  hidden 
below  the  horizon.  Others  maintain  that,  since  it 
has  been  seen  in  tropical  regions  in  the  east  and 
west  simultaneously,  it  can  be  explained  only  on  the 
theory  of  a  "nebulous  ring  that  surrounds  the  earth 
within  the  orbit  of  the  moon." 


the  Sidereal  jfetqm. 


"He  telleth  the  number  of  the  stars;  He  calleth  them  all  by 
their  names." 

PSALM  cxlvii.  4. 


THE  SIDEREAL  SYSTEM. 


THE  STAKS. 

IN  our  celestial  journey  we  have  reached  Neptune, 
the  sentinel  outpost  of  the  solar  system.  "We  are 
now  2,750  millions  of  miles  from  our  sun.  Yet  we 
are  apparently  no  nearer  the  fixed  stars  than  when 
we  first  started.  They  twinkle  as  serenely  there  in 
the  far-off  sky  as  to  us  here  on  the  earth.  The 
heavens  by  night,  with  the  exception  of  a  few 
changes  in  the  planets,  look  perfectly  familiar. 
Between  them  and  us  there  is  a  vast  chasm  which 
no  imagination  can  bridge ;  a  distance  so  immense 
that  figures  are  meaningless,  and  we  can  only  call 
it  space, — so  profound  that  to  us  it  is  limitless,  though 
beyond  we  see  other  worlds  twinkling  like  distant 
lights  over  a  waste  of  waters. 

WE  NEVER  SEE  THE  STABS. — This  assertion  seems 
almost  paradoxical,  yet  it  is  strictly  true.  So  far 
are  the  stars  removed  from  us,  that  we  see  only  the 
light  they  send,  but  not  the  surface  of  the  worlds 
themselves.  They  are  merely  glittering  points  of 


222  THE  SIDEREAL  SYSTEM. 

light.  The  most  powerful  telescope  fails  to  produce 
a  sensible  disk.  This  constitutes  a  marked  point 
of  difference  between  a  planet  and  a  fixed  star. 

THE  ANNUAL  PARALLAX  OF  THE  FIXED  STARS. — When 
speaking  of  this  subject  on  page  139,  we  said  that 
183,000,000  miles,  or  the  diameter  of  the  earth's 
orbit,  is  taken  as  the  unit  for  measuring  the  par- 
allax of  the  fixed  stars.  Yet  when  the  stars  are 
viewed  from  even  these  extreme  points,  they  mani- 
fest so  very  slight  a  change  of  place,  that  to  esti- 
mate it  is  one  of  the  most  delicate  feats  of  astron- 
omy.* At  the  present  time,  it  is  considered  that 
the  star  Alpha  (a)  Centauri  in  the  southern  heavens 
is  the  nearest  to  the  earth.  Its  parallax  is  judged 
to  be  about  1".  Its  distance  is  more  than  200,000 
times  that  of  the  earth  from  the  sun,  or  nineteen  tril- 
lions of  miles.  This  is  probably  by  no  means  its  ex- 
treme distance,  but  merely  the  limit  ivithin  which 
it  cannot  be,  but  beyond  which  it  must  be.  These 
figures  convey  to  our  mind  no  idea  of  distance.  Our 
imagination  fails  to  grasp  the  thought,  or  to  picture 
the  vast  void  across  which  we  are  gazing.  We 
remember  that  light  moves  at  the  wonderful  rate 
of  183,000  miles  per  second.  A  ray  at  this  speed 
would  plunge  out  into  the  abyss  beyond  Neptune, 
in  one  day,  six  times  the  distance  of  that  planet 

*  Prof.  Airy  says  the  star  which  gives  the  greatest  parallax 
of  any,  presents  the  same  angle  as  that  at  which  a  circle  six- 
tenths  of  an  inch  in  diameter  would  be  seen  at  the  distance  of 
a  mile  1 


THE  STABS.  223 

from  the  sun.  Yet  it  must  sweep  on  at  this  prodig- 
ious speed,  day  and  night,  for  three  years  and  nine 
months  to  span  the  gulf  and  reach  a  stopping  point 
at  the  nearest  fixed  star.  "To  a  spectator  standing 
at  a  Centauri,  the  entire  diameter  of  the  earth's 
orbit  would  be  hidden  by  a  thread  -fa  of  an  inch  in 
diameter,  held  at  a  distance  of  650  feet  from  the 
eye."  That  is  to  say,  a  line  183,000,000  miles  long, 
looked  at  broadside,  would  shrink  into  a  mere  point. 
If  our  sun  were  removed  to  that  distance,  it  would 
shine  with  a  light  only  equal  to  that  of  the  north 
polar  star,  and  would  take  its  place  among  the  con- 
stellations as  a  fixed  star. 

This,  we  must  remember,  is  the  distance  of  the 
nearest  fixed  star.  It  has  been  estimated  that  the 
average  time  required  for  the  light  of  the  smallest 
stars  which  are  visible  to  the  naked  eye  to  reach  the 
earth  is  about  125  years.  What,  then,  shall  we  say 
of  those  far-distant  ones,  whose  faint  light  appears 
as  a  mere  fleecy  whiteness  even  in  the  most  power- 
ful telescopes  ?  The  conclusion  is  irresistible,  that 
the  light  we  receive  set  out  on  its  sidereal  journey 
far  back  in  the  past,  perhaps  before  the  creation  of 
man! 

MOTION  OF  THE  FIXED  STABS. — It  will  aid  us  still 
further  in  comprehending  the  immense  distances  of 
the  stars,  to  learn  that  though  they  seem  to  be  fixed, 
yet  they  are  moving  much  more  swiftly  than  any  of 
the  planets.  Thus,  Arcturus  flies  through  space  at 
the  astonishing  rate  of  about  200,000  miles  per  hour, 


224  THE   SIDEREAL  SYSTEM. 

or  nearly  twice  that  of  Mercury,  and  more  than  three 
times  that  of  the  earth.  Yet,  through  all  our  life- 
time, we  shall  never  be  able  to  detect  any  change  in 
its  position.  It  requires  three  centuries  for  it  to 
move  over  the  starry  vault  a  space  equal  to  the 
moon's  apparent  diameter. 

THE  STABS  ARE  SUNS. — The  vast  distance  at  which 
they  are  known  to  be,  precludes  the  thought  of  their 
shining,  like  the  planets  or  the  moon,  by  reflecting 
back  the  light  of  our  sun.  They  must  be  self-lumin- 
ous, and  are  doubtless  each  the  centre  of  a  system 
of  planets  and  satellites. 

OUR  SUN  A  STAR. — As  we  see  only  the  suns  of  these 
distant  systems,  so  their  inhabitants  see  only  the 
sun  of  ours,  and  that  as  a  small  star. 

OUR  SYSTEM  ITSELF  IN  MOTION. — Like  all  the  other 
stars,  our  sun  is  in  motion.  It  is  sweeping  onward, 
with  its  retinue  of  worlds,  150,000,000  miles  per  year, 
toward  a  point  in  the  constellation  Hercules.  The 
Pleiades  are  thought  to  be  the  centre  around  which 
this  great  movement  is  taking  place,  but  the  orbit  is 
so  vast  and  the  centre  so  remote,  that  nothing  defi- 
nite is  yet  known. 

THE  NUMBER  OF  THE  FIXED  STARS. — As  we  look  at 
the  heavens  on  a  clear  night,  the  stars  seem  almost 
innumerable.  To  count  them,  one  would  think  al- 
most as  interminable  a  task  as  to  number  the  leaves 
on  the  trees.  It  is,  therefore,  somewhat  startling  to 
learn  that  the  entire  number  visible  to  the  most 
piercing  eyesight,  does  not  exceed  6,000,  while  few 


THE  STARS. 


225 


can  discern  more  than  4,000.  This  illusion  may  be 
easily  explained,  when  we  remember  how  the  impres- 
sion of  a  bright  light  remains  upon  the  retina,  as  in 
the  whirling  of  a  firebrand.  However,  the  number 


Fie.  70. 


A  PART  OF  THE  CONSTELLATION  OF  THE  TWTKfl. 

which  may  be  seen  with  a  telescope  becomes  alto- 
gether marvellous.     In  the  cut  is  shown  a  portion 


226  THE  SIDEREAL  SYSTEM. 

of  the  heavens  where  the  naked  eye  sees  but  sis 
stars.  Could  we  examine  the  same  region  of  the 
sky  with  more  powerful  instruments,  new  constella- 
tions would  doubtless  be  descried  in  the  infinite 
depths  of  space. 

SCINTILLATION. — The  twinkling  of  the  fixed  stars  is 
due  to  what  is  termed  in  Natural  Philosophy  "  the 
interference  of  light."  The  air  being  unequally 
dense,  warm,  and  moist  in  its  various  strata,  trans- 
mits very  irregularly  the  different  colors  of  which 
white  light  is  composed.  Now  one  color  prevails 
over  the  rest,  and  now  another,  so  that  the  star  ap- 
pears to  change  color  incessantly.  As  the  purity 
of  the  air  varies,  the  twinkling  of  the  stars  also 
changes,  although  it  is  always  greatest  near  the 
horizon.  Humboldt  says  that  at  Cumana,  in  South 
America,  where  the  air  is  remarkably  pure  and  uni- 
form in  density,  the  stars  cease  to  twinkle  after  they 
have  risen  15°  above  the  horizon.  This  gives  to 
the  celestial  vault  a  peculiarly  calm  and  soft  appear- 
ance. 

MAGNITUDE  OF  THE  STARS. — As  the  telescope  re- 
veals no  disk  of  even  the  nearest  stars,  we  know 
nothing  of  their  comparative  size.  The  finest  spi- 
der's web,  placed  at  the  focus  of  the  instrument, 
hides  the  star  from  the  eye.  When  the  moon  passes 
in  front  of  a  star,  the  occultation  is  instantaneous, 
and  not  gradual,  as  in  the  case  of  the  planets.  Clas- 
sification depends,  therefore,  upon  their  relative 
brightness.  The  most  conspicuous  are  termed  stars 


THE  STABS.  227 

of  the  first  magnitude.  There  are  about  twenty  of 
these.  The  number  of  second  magnitude  stars  in 
the  entire  heavens  is  about  sixty-five ;  of  the  third, 
about  200 ;  of  the  fifth,  1,100 ;  and  of  the  sixth, 

Fig.  71. 


3,200.  Few  persons  can  see  any  smaller  stars  than 
those  of  the  fifth  or  sixth  magnitude.  The  ordinary 
telescope  shows  faint  stars  down  to  the  tenth,  while 
the  more  powerful  instruments  reveal  those  as  low 
as  the  twentieth  magnitude. 

THE  CAUSE  OF  THE  DIFFERENCE  IN  THE  BRIGHTNESS 
OF  THE  STARS. — This  may  result  from  a  difference  in 
their  distance,  size,  or  intrinsic  brightness.  Whence 
it  follows  that  the  faintest  stars  may  not  be  the  most 
distant  from  the  earth. 

NAMES  OF  THE  STARS. — Many  of  the  brightest  stars 
received  proper  names  at  an  early  date ;  as  Sirius, 
Arcturus.  The  stars  of  each  constellation  are  dis- 
tinguished by  the  letters  of  the  Greek  alphabet ;  the 
brightest  being  usually  called  Alpha,  the  next  Beta 
etc., — the  name  of  the  constellation,  in  the  genitive 
case,  being  put  after  each.  Ex.,  a  Arietis,  fi  Lyras.* 

*  This  means  a  of  Aries,  /3  of  Lyra;  the  genitive  case  in  Latin 
being  equivalent  to  the  preposition  of. 


228 


THE   SIDEREAL  SYSTEM. 


THE  GREEK 

ALPHABET. 

A 

a 

Alpha 

N 

V 

Nu 

B 

# 

Beta 

H 

I 

Xi 

r 

7 

Gamma 

0 

0 

Omicron 

A 

6 

Delta 

n 

<x 

Pi 

E 

i 

Epsilon 

p 

P 

Rho 

Z 

r 

Zeta 

2 

s- 

Sigma 

H 

>? 

Eta 

T 

r 

Tau 

0 

0 

Theta 

T 

u 

Upsilon 

I 

I 

Iota 

$ 

9 

Phi 

K 

X 

Kappa 

X 

X 

Chi 

A 

X 

Lambda 

* 

4, 

Psi 

M 

* 

Mu 

ft 

CO 

Omega 

When  the  Greek  letters  are  exhausted,  the  Roman 
alphabet  is  used  in  the  same  way.  Star  catalogues 
are  issued,  containing  the  stars  arranged  in  the 
order  of  their  Right  Ascension,  and  numbered  for 
convenience  of  reference.  Argelander's  Charts  have 
300,000  stars  marked  in  the  northern  hemisphere. 

THE  CONSTELLATIONS.— From  the  earliest  ages,  the 
stars  have  been  arranged  in  constellations,  for  the 
purpose  of  more  readily  distinguishing  them.  Some 
of  these  groups  were  named  from  their  supposed  re- 
semblance to  some  figures,  such  as  perching  birds, 
pugnacious  bulls,  or  contorted  snakes,  while  others 
do  honor  to  the  memory  of  the  classic  heroes  of  an- 
tiquity. 

"  Thus  monstrous  forms,  o'er  heaven's  nocturnal  arch, 
Seen  by  the  sage,  in  pomp  celestial  march ; 


THE  STABS.  229 

See  Aries  there  his  glittering  bow  unfold, 
And  raging  Taurus  toss  his  horns  of  gold ; 
With  bended  bow  the  sullen  Archer  lowers, 
And  there  Aquarius  comes  with  all  his  showers; 
Lions  and  Centaurs,  Gorgons,  Hydras  rise, 
And  gods  and  heroes  blaze  along  the  skies." 

With  a  few  exceptions,  the  likeness  is  purely  fan- 
ciful. The  heavens  are  much  less  of  a  menagerie 
than  a  celestial  atlas  would  make  them  appear. 
The  division  into  constellations  is  a  mere  relic  of 
barbarism,  entirely  unworthy  of  modern  civilization. 
Not  only  are  the  figures  uncouth,  and  the  origin 
often  frivolous,  but  the  boundaries  are  not  distinct. 
Stars  often  occur  under  different  names ;  while  one 
constellation  encroaches  upon  another.  As  Cham- 
bers well  remarks,  "  Aries  should  not  have  a  horn  in 
Pisces  and  a  leg  in  Cetus,  nor  should  13  Argos  pass 
through  the  Unicorn's  flank  into  the  Little  Dog.  51 
Camelopardali  might  with  propriety  be  extracted 
from  the  eye  of  Auriga,  and  the  ribs  of  Aquarius  re- 
leased from  46  Capricorni."  While,  however,  the 
constellations  are  thus  rude  and  imperfect,  there 
seems  little  hope  of  any  change.  Age  gives  them  a 
dignity  that  insures  their  perpetuation. 

INVENTION  OF  THE  CONSTELLATIONS. — This  goes 
back  into  ages  of  which  no  record  remains.  By 
some  it  has  been  ascribed  to  the  Greeks.  When  the 
signs  of  the  zodiac  were  named,  they  doubtless  coin- 
cided with  the  constellations.  Aries  (the  ram)  was 
so  called  because  it  rose  with  the  sun  in  the  spring- 
time, and  the  Chaldean  shepherds  named  it  from 


230  THE   SIDEREAL  SYSTEM. 

their  flocks,  their  most  valued  possession.  Then  fol- 
lowed in  order  Taurus  (the  bull)  and  Gemini  (the 
twins),  called  from  the  herds,  which  were  esteemed 
next  in  value.  At  the  summer  solstice  the  sun  ap- 
pears to  stop,  and,  crab-like,  to  crawl  backward; 
hence  the  name  Cancer  (the  crab).  When  the  sun 
is  in  Leo,  the  brooks  being  dry,  the  lion  leaves  his 
lurking-place  and  becomes  a  terror  to  all.  Virgo 
comes  next,  when  the  virgins  glean  in  the  summer 
harvest.  At  the  autumnal  equinox  the  days  and 
nights  are  equally  balanced,  and  this  is  beautifully 
represented  by  Libra  (the  scales).  The  vegetation 
decays  in  the  fall,  causing  sickness  and  death  ;  the 
Scorpion,  that  stings  as  it  recedes,  is  suggestive  oi 
this  Parthian  warfare.  Sagittarius  (the  archer)  tells 
of  the  hunting  month.  Capricornus  (the  goat), 
which  delights  in  climbing  lofty  precipices,  denotes 
how  at  the  winter  solstice  the  sun  begins  to  climb 
the  sky  on  his  return  north.  Aquarius  (the  water- 
bearer)  is  a  natural  emblem  of  the  rainy  season. 
Pisces  (the  fishes)  is  the  month  for  fishing. 

SIGNS  AND  CONSTELLATIONS  DO  NOT  AGREE.  —  By 

the  precession  of  the  equinoxes,  as  we  have  before 
described  on  page  121,  the  signs  have  fallen  back 
along  the  ecliptic  about  30°,  so  that  those  stars 
which  were,  in  the  infancy  of  astronomy,  in  the  sign 
Aries  (T)  are  now  in  Taurus  (8),  and  those  which 
were  in  the  sign  Pisces  (  K  )  are  now  in  Aries 


*  If  the  teacher  put  a  pin  at  the  centre  of  Fig.  72,  and,  drawing  a  sharp 
kuife  between  the  eignu  and  the  constellations?,  cause  the  inner  part  to  re- 
volve, the  si^ns  may  be  turned  before  any  constellation,  aud  thus  thie  change 
he  clearly  apprehended. 


THE   SIGNS. 


231 


The  accompanying  cut  may  illustrate  this  more 
clearly. 

Fig.  72. 


S  AND  CONSTELLATIONS,  AS  THEY  NOW  COMPARE    IN   THE 
HEAVENS,  THE  FORMER  HAVING  FALLEN  BACK,  AND  THE 
LATTER  APPARENTLY  ADVANCED,  30°  EACH. 


PERMANENCE  OF  THE  CONSTELLATIONS. — The  figures 
which  the  stars  form,  and  the  general  appearance  of 
the  constellations,  are  due  to  the  position  we  occupy. 
Could  we  cross  the  gulf  of  space  beyond  Neptune, 
the  stars  now  so  familiar  to  us  would  look  strangely 
enough  in  their  new  groupings.  As  one  in  riding 
through  a  forest  sees  the  trees  apparently  increase 
in  size  and  open  up  to  view  before  him,  while  they 


232  THE  SIDEREAL  SYSTEM. 

decrease  in  size  and  close  in  behind  him,  forming 
clusters  and  groups  which  constantly  change  as  he 
passes  along ;  so,  as  our  earth  travels  with  the  solar 
system  on  its  immense  sidereal  journey,  the  stars 
will  grow  larger  and  brighter  in  front,  while  those 
behind  us  will  appear  smaller  and  dimmer.  Since, 
in  addition  to  this,  the  stars  themselves  are  in  mo- 
tion with  varying  velocity  and  in  different  directions, 
the  constellations  must  change  still  more  rapidly,  so 
as  ultimately  to  transform  entirely  the  appearance  of 
the  heavens.  In  time,  the  "  bands  of  Orion"  will 
be  loosened,  and  the  "Seven  Sisters"  will  glide 
apart  into  remote  space.  Such  are  the  dibtances 
however,  that,  although  these  movements  have  been 
going  on  constantly,  yet  since  the  creation  of  man 
no  variation  has  occurred  that  is  perceptible,  save  to 
the  watchful  astronomer.  Nothing  in  nature  is  as 
invariable  as  the  stars.  They  are  the  standards  of 
time.  Myriads  of  years  must  elapse  before  new  star- 
maps  will  be  required.  We  need  not,  then,  allow  any 
fear  of  confusion  to  disturb  us  while  we  study  the 
sky  as  it  is. 

VALUE  OF  THE  STARS  IN  PRACTICAL  LIFE.  — "  The 
stars  are  the  landmarks  of  the  universe."  They  seem 
to  be  placed  in  the  heavens  by  the  Creator,  not  alone 
to  elevate  our  thoughts  and  expand  our  conceptions 
of  the  infinite  and  eternal,  but  to  afford  us,  amid  the 
constant  fluctuations  of  our  own  earth,  something 
unchangeable  and  abiding.  Every  landmark  about 
us  is  constantly  changing,  but  over  all  shine  the 


THE  STAKS.  233 

"eternal  stars,"  each  with  its  place  so  accurately 
marked,  that  to  the  astronomer  and  geographer  no 
deception  is  possible.  To  the  mariner,  the  heavens 
become  a  dial-plate,  the  figures  on  its  face  set  with 
glittering  stars,  along  which  the  moon  travels  as  a 
shining  hand  that  marks  off  the  hours  with  an  accu- 
racy no  clock  can  ever  rival.  Standing  on  the  deck 
of  his  vessel,  far  out  at  sea,  a  single  observation  of 
the  sun  or  stars  decides  his  location  in  the  waste  of 
waters  as  accurately  as  if  he  were  at  home,  and  had 
caught  sight  of  some  old  landmark  he  had  known 
from  his  boyhood.  In  all  the  intricacies  of  survey- 
ing, the  stars  furnish  the  only  immutable  guide. 
Our  clocks  vainly  strive  to  keep  time  with  the  celes- 
tial host.  Thus,  by  a  wise  provision  of  Providence, 
even  in  the  most  common  affairs  of  life,  are  we  com- 
pelled to  look  for  guidance  from  the  shifting  objects 
of  earth  up  to  the  heavens  above. 

THE  VIEWS  OF  THE  ANCIENTS. — Standing  in  the  light 
of  our  present  knowledge,  the  ideas  of  the  ancients 
seem  almost  incredible,  and  we  can  hardly  under- 
stand how  they  could  have  been  seriously  enter- 
tained. Anaximenes  (550  B.  c.)  thought  that  the  stars 
were  for  ornament,  and  were  nailed  like  bright  studs 
into  the  crystalline  sphere.  Anaxagoras  (450  B.  c.) 
considered  that  they  were  stones  whirled  up  from  the 
earth  by  the  rapid  motion  of  the  ether  around  us, 
and  that  its  inflammable  properties  set  them  on  fire 
and  caused  them  to  shine  as  stars.  Many  schools 
of  the  Grecian  philosophers — the  Stoics,  Epicu- 


234  THE  SIDEREAL  SYSTEM. 

reans,  etc. — believed  that  they  were  celestial  fires  kept 
alive  by  matter  that  constantly  streamed  up  to  them 
from  the  centre  of  the  heavens.  The  stars  were  at 
one  time  said  to  feed  on  air ;  at  another,  to  be  the 
breathing  holes  of  the  universe. 

THREE  ZONES  OF  STARS. — If  we  recall  what  was  said 
on  page  104,  concerning  the  paths  of  the  stars  and 
appearance  of  the  heavens  at  different  seasons  of 
the  year,  we  shall  see  that  the  constellations  are  nat- 
urally divided  into  three  zones.  The  first  embraces 
those  which  are  visible  through  the  entire  year ;  the 
second,  those  whose  orbits  can  be  seen  only  in  part 
on  any  given  night ;  and  the  third,  those  whose  paths 
just  graze  our  southern  horizon,  or  never  pass 
above  it. 

THE  CONSTELLATIONS. 

NORTHERN  CIRCUMPOLAR  CONSTELLATIONS. — These 
constellations  in  our  latitude  are  visible  every 
night.  They  may  be  easily  traced  by  holding  the 
book  up  toward  the  northern  sky  in  such  a  way 
that  Polaris  and  the  Dipper  on  the  map  and  in  the 
heavens  agree  in  position,  and  then  locating  the 
other  constellations  by  comparison.  As  they  revolve 
about  Polaris,  their  places  will  vary  with  every 
successive  night  through  the  year.  The  cut  repre- 
sents them  as  they  are  seen  at  midnight  of  the  win- 
ter solstice.  At  6  P.  M.  of  that  day  the  right-hand 
side  of  the  map  should  be  held  downward,  and  the 


THE    CIRCUMPOLAB   CONSTELLATIONS.  235 

Big  Dipper  will  be  directly  below  the  north  star. 
At  6  A.  M.  the  left-hand  side  should  be  at  the  bot- 
tom, and  the  Dipper  will  be  above  Polaris.  From 
day  to  day  this  aspect  will  change,  each  star  coming 

(Map  No.  1.)— Fig.  73. 


NORTHERN  CIRCTJMPOLAR  CONSTELLATIONS. 

a  little  earlier  to  the  meridian,  or  to  its  position  on 
the  preceding  night.  The  rate  of  this  progression 
is  six  hours,  or  90°,  in  three  months. 

Ursa  Major  is  represented  under  the  figure  of  a 
great  bear.  It  contains  138  stars  visible  to  the 
naked  eye.  The  constellation  has  been  celebrated 


236  THE  SIDEREAL  SYSTEM. 

among  all  nations.  It  is  remarkable  that  the  shep- 
herds of  Chaldea  in  Asia,  and  the  Iroquois  Indians 
of  America,  gave  to  it  the  same  name. 

Principal  stars. — A  noticeable  cluster  of  seven 
stars — six  of  the  second  and  one  of  the  fourth  mag- 
nitude— forms  what  is  familiarly  termed  "  The  Dip* 
per."  In  England  it  is  styled  Charles's  Wain,  from 
a  fancied  resemblance  to  a  wagon  drawn  by  three 
horses  tandem.  Mizar  (£)  has  a  minute  companion, 
Alcor,  which  Humboldt  tells  us  could  be  rarely 
seen  in  Europe.  A  person  with  good  eyesight  may 
now  readily  detect  it.  Megrez  (£),  at  the  junction  of 
the  handle  and  the  bowl,  is  to  be  marked  particu- 
larly, since  it  lies  almost  exactly  in  the  colure  passing 
through  the  autumnal  equinox.  Dubhe  and  Merak 
are  termed  "  The  Pointers"  since  they  always  point 
out  the  polar  star.  The  bear's  right  fore  paw  and 
hinder  paw  are  each  marked  by  two  small  stars,  as 
shown  in  the  cut ;  a  similar  pair  nearly  in  line  with 
these  denote  the  left  hinder  paw  (see  £,  Fig.  76). 
The  pairs  are  15°  apart. 

Mythological  history. — Diana  had  a  very  beau- 
tiful attendant  named  Callisto.  Juno,  the  queen  of 
heaven,  becoming  jealous  of  the  maid,  transformed 
her  into  a  bear. 


The  prostrate  wretch  lifts  up  her  head  in  prayer, 
Her  arms  grow  shaggy,  and  deformed  with  hair ; 
Her  nails  are  sharpened  into  pointed  claws, 
Her  hands  hear  half  her  weight  and  turn  to  paws. 
Her  lips,  that  once  would  tempt  a  god,  begin 
To  grow  distorted  in  an  ugly  grin. 


THE  CIRCUMPOLAR  CONSTELLATIONS.  237 

And  lest  the  supplicating  brute  might  reach 
The  ears  of  Jove,  she  was  deprived  of  speech. 
How  did  she  fear  to  lodge  in  woods  alone, 
And  haunt  the  fields  and  meadows  once  her  own  i 
How  often  would  the  deep-mouthed  dogs  pursue, 
Whilst  from  her  hounds  the  frighted  hunters  flew. 

Some  time  afterward,  Callisto's  son,  Areas,  being 
out  hunting,  pursued  his  mother  and  was  about  to 
transfix  her  with  his  uplifted  spear,  when  Jupiter  in 
pity  transferred  them  both  to  the  heavens,  and 
placed  them  among  the  constellations  as  Ursa  Ma- 
jor and  Ursa  Minor. 

Ursa  Minor  is  represented  under  the  figure  of  a 
small  bear.  It  contains  twenty-four  stars,  of  which 
only  three  are  of  the  third,  and  four  of  the  fourth 
magnitude. 

Principal  stars. —  A  cluster  of  seven  stars  forms 
what  is  termed  the  "  Little  Dipper"  Three  of  them 
are  small,  and  are  seen  with  difficulty.  Polaris,  at 
the  extremity  of  the  handle,  has  been  known  from 
time  immemorial  as  the  North  Polar  Star.  Among 
the  Greeks  it  was  styled  Cynosure.  Until  the  ma- 
riner's compass  came  into  use,  it  was  the  star 

•     "  Whose  faithful  beams  conduct  the  wandering  ship 
Through  the  wide  desert  of  the  pathless  deep." 

Polaris  does  not  mark  the  exact  position  of  the 
pole,  since  that  is  about  1  J°  toward  the  Pointers. 
This  distance  will  gradually  diminish,  until  in  time 
it  will  be  only  J° :  then  it  will  increase  again,  until 
in  the  lapse  of  ages — 12,000  years  hence — the  bril- 


238  THE  SIDEREAL  SYSTEM. 

liant  star  a  Lyrse  will  fulfil  the  office  of  polar  star 
for  those  who  shall  then  live  on  the  earth. 

Curious  fact  concerning  the  Pyramids. — Of  the 
nine  Pyramids  which  are  standing  at  Gizeh,  Egypt, 
six  have  openings  facing  the  north.  These  lead  to 
straight  passages  which  descend  at  a  uniform  angle 
of  about  26°  and  are  parallel  with  the  meridian.  If 
we  suppose  a  person,  4000  years  ago,  standing  at 
the  lower  end  of  one  of  these  passages,  and  looking 
out,  his  eye  would  strike  the  sky  near  the  star 
Thuban,  which  was  then  the  polar  star.  The 
supposed  date  of  the  building  of  these  Pyramids 
(2123  B.  c.)  agrees  with  that  epoch,  and  very  naturally 
suggests  that  the  builders  had  some  special  design 
in  this  peculiar  construction. 

The  distance  of  Polaris  is  so  great,  that  though  the 
star  is  moving  through  space  at  the  rate  of  ninety 
miles  per  minute,  this  tremendous  speed  is  imper- 
ceptible to  us.  It  requires  nearly  fifty  years  for  its 
light  to  reach  the  earth ;  so  that  when  we  look  at  Po- 
laris, we  know  that  the  ray  which  strikes  our  eye 
set  out  on  its  journey  through  space  half  a  cen- 
tury ago.  We  cannot  state  positively  that  the  star 
is  now  in  existence,  since  if  it  were  destroyed  to-day 
it  would  be  fifty  years  before  we  should  miss  it. 

Calculation  of  latitude  from  Polaris. — By  an  ob- 
server at  the  equator,  Polaris  is  seen  at  the 
horizon.  If  he  advances  north,  the  horizon  is  de- 
pressed and  Polaris  seems  to  rise  in  the  heavens. 
When  it  has  reached  the  height  of  a  degree,  the  ob- 


THE    CIRCUMPOLAB  CONSTELLATIONS.  239 

server  is  said  to  have  passed  over  a  degree  of  lati- 
tude on  the  earth's  surface.  As  he  moves  further 
north,  the  polar  star  continues  to  ascend ;  its  dis- 
tance above  the  horizon  denoting  the  latitude  of 
each  place  in  succession,  until  at  the  north  pole,  if 
one  could  reach  that  point,  Polaris  would  be  seen 
directly  overhead. 

Draco  is  represented  under  the  figure  of  a  long 
sinuous  serpent,  stretching  between  Ursa  Major  and 
Ursa  Minor,  nearly  encircling  the  latter  constellation, 
and  finally  reaching  out  its  head  almost  to  ;he  body 
of  Hercules. 

Principal  stars. — Four  small  stars  form  a  quad- 
rilateral figure  at  the  head;  a  fifth  of  the  fourth 
magnitude  which  is  scarcely  visible,  marks  the 
end  of  the  nose  ;  several  scattered  groups  and  deli- 
cate triangles  of  small  stars,  denote  the  position  of 
the  various  coils  of  the  body ;  thence,  an  irregular 
line  of  stars  traces  the  dragon's  tail  around  between 
Ursa  Major  and  Ursa  Minor.  Thuban  lying  midway 
between  y  of  the  Little  Dipper  and  £  of  the  Big  Dip- 
per, is  noted  as  the  polar  star  of  forty  centuries  ago. 

Mythological  history. — Many  accounts  are  given  of 
the  origin  of  this  constellation,  as  indeed  there  are  of 
almost  every  one  in  the  heavens.  The  prevalent 
opinion  is,  that  it  is  the  dragon  which  Cadmus  slew. 
The  story  is  as  follows.  Jupiter  had  carried  off  Eu- 
ropa.  Agenor,  her  father,  sent  her  brother  Cadmus 
in  pursuit  of  his  lost  sister,  bidding  him  not  to  re- 
turn until  he  was  successful  in  his  search.  After  a 


240  THE  SIDEREAL  SYSTEM. 

time,  Cadmus,  weary  of  his  wanderings,  inquired  of 
the  oracle  of  Apollo  concerning  the  fate  of  Europa. 
He  was  told  to  cease  looking  for  his  sister,  to  fol- 
low a  cow  as  a  guide,  and  when  she  rested,  there 
to  build  a  city.  Hardly  had  Cadmus  stepped  out 
of  the  temple,  when  he  saw  a  cow  slowly  walking 
along.  He  followed  her  until  she  came  upon  the 
broad  plains  where  Thebes  afterward  stood.  Here 
she  stopped.  Cadmus  wishing  to  offer  a  sacrifice  to 
Jupiter  in  gratitude  for  the  delightful  location,  sent 
his  servants  to  seek  for  water.  In  a  dense  grove 
near  by  was  a  fountain  guarded  by  a  fierce  dragon 
(DRACO),  and  sacred  to  Mars.  The  Tyrians  approach- 
ing this  and  attempting  to  dip  up  some  water,  were 
attacked,  and  many  of  them  killed  by  that  enormous 
serpent,  whose  head  overtopped  the  tallest  trees. 
Cadmus,  becoming  impatient,  went  in  search  of  his 
men,  and  on  coming  to  the  spring,  saw  the  sad  disas- 
ter. He  forthwith  fell  upon  the  monster,  and  after  a 
severe  battle  succeeded  in  slaying  him.  While  stand- 
ing over  his  conquered  foe,  he  heard  a  voice  from 
the  ground  bidding  him  take  the  dragon's  teeth  and 
sow  them.  He  obeyed.  Scarcely  had  he  finished 
ere  the  earth  began  to  move  and  the  points  of  spears 
to  prick  through  the  surface.  Next  nodding  plumes 
shook  off  the  clods,  and  the  heads  of  armed  men  pro- 
truded. Soon  a  great  harvest  of  warriors  covered 
the  entire  plain.  Cadmus,  in  terror  at  the  appear- 
ance of  these  giants,  whom  he  termed  Sparti  (the 
Sown),  prepared  to  attack  them,  when  suddenly  they 


THE   CIECUMPOLAE   CONSTELTATIONS.  241 

turned  upon  themselves,  and  never  ceased  their  war- 
fare until  only  five  of  the  crowd  survived.  These 
making  peace  with  each  other,  joined  Cadmus  and 
assisted  him  in  building  the  city  of  Thebes. 

Cephetts  is  represented  as  a  king  in  regal  state, 
with  a  crown  of  stars  on  his  head,  while  he  holds  in 
Ids  hand  a  sceptre  which  is  extended  toward  his 
wife,  Cassiopeia.  The  constellation  contains  thirty- 
five  stars  visible  to  the  naked  eye. 

Principal  stars. — The  brightest  star  is  Alderamin 
(«),  in  the  right  shoulder.  Alphirk  (/3),  in  the  girdle, 
is  at  the  common  vertex  of  several  triangles,  which 
point  out  respectively  the  left  shoulder  (t),  the  left 
knee  (7),  and  the  right  foot.  The  head,  which  lies 
in  the  Milky  Way,  is  marked  by  a  delicate  little 
triangle  of  three  stars.  This  forms,  with  «,  /3,  and  *, 
quite  a  regular  quadrilateral  figure.  A  bright  little 
star  of  the  fifth  magnitude,  close  to  Polaris,  points 
out  the  left  foot. 

Cassiopeia*  is  represented  as  a  queen  seated  on 
her  throne.  On  her  right  is  the  king,  on  her  left 
Perseus,  her  son-in-law,1  and  above  her  is  Androme- 
da, her  daughter.  The  constellation  contains  fifty- 
five  stars  visible  to  the  naked  eye. 

Principal  stars. — A  line  drawn  from  Megrez  (5),  in 
Ursa  Major,  through  Polaris  and  continued  an  equal 
distance  beyond,  will  strike  Caph  ((3)  in  Cassiopeia. 
This  star  is  noticeable  as  marking,  with  the  others 

*  For  mythological  history,  see  Perseus  and  Andromeda. 
U 


242  THE   SIDEREAL   SYSTEM. 

named,  the  equinoctial  colure,  and  as  being  on  the 
same  side  of  the  true  pole  as  Polaris.  The  principal 
stars  form  the  figure  of  an  inverted  chair,  which  is 
very  striking  and  may  be  easily  traced. 

EQUATORIAL  CONSTELLATIONS. 

The  constellations  we  shall  now  describe  lie  south 
of  the  circumpolar  groups.  Only  a  portion  of  their 
paths  is  above  our  horizon.  In  using  the  maps,  tho 
observer  is  supposed  to  stand  with  his  back  toward 
Polaris,  and  to  be  looking  directly  south.  Com- 
mencing with  the  constellation  Perseus,  so  intimately 
connected  with  the  other  members  of  the  royal  fam- 
ily just  described,  we  pass  eastward  in  our  survey 
and  notice  the  various  constellations  as  they  slowly 
defile  in  silent  march  across  the  sky.  The  first  map 
represents  the  constellations  on  or  near  the  meridian 
at  nine  o'clock  in  the  evening  of  the  winter  solstice. 
On  the  evening  of  the  autumnal  equinox,  the  left- 
hand  side  of  the  map  should  be  turned  downward 
toward  the  eastern  horizon.  On  the  evening  of  the 
vernal  equinox,  the  right-hand  side  should  be  turned 
to  the  western  horizon.  At  these  different  times,  the 
stars,  though  preserving  their  relative  positions,  will 
be  diversely  inclined  to  the  horizon.  As  the  stars 
apparently  move  westward  at  the  rate  of  15°  per 
hour,  the  time  of  the  evening  determines  what  stars 
\\ill  be  visible,  anx]  also  their  distances  above  the 
honzon, 


EQUATORIAL  CONSTELLATIONS.         248 

(Map  No.  2)— Fig.  74. 


Perseus  is  represented  as  brandishing  an  enor- 
mous sword  in  his  right  hand,  while  in  his  left  he 
holds  the  head  of  Medusa.  The  constellation  com- 
prises eighty-one  stars  visible  to  the  naked  eye. 

Principal  stars. — The  most  prominent  figure  is 
called  the  segment  of  Perseus.  It  consists  of  several 
stars  arranged  in  a  line  curving  toward  Ursa  Major. 
Algenib  («),  the  brightest  of  .these,  is  of  the  second 
magnitude.  Algol,  in  the  midst  of  a  group  of  small 
stars,  marks  the  head  of  Medusa.  Between  the 
bright  stars  of  Perseus  and  Cassiopeia  is  a  beautiful 
star-cluster  visible  to  the  naked  eye. 

Mythological  history. — Perseus,  from  whom  this 
constellation  was  named,  was  the  son  of  Jupiter  and 
Danae.  His  grandfather,  Acrisius,  having  been  in- 
formed by  the  oracle  that  his  grandson  would  be  the 


2J4  THE   SIDEREAL  SYSTEM. 

instrument  of  Lis  death,  put  the  mother  and  child  in 
a  coffer  and  set  them  adrift  on  the  sea.  Fortunately, 
they  floated  near  the  island  Seriphus,  where  they 
were  rescued  and  kindly  treated  by  a  brother  of  Pol- 
ydectes,  king  of  the  country.  When  Perseus  had 
grown  up,  he  was  ordered  by  Polydectes  to  bring 
him,  as  a  marriage  gift,  the  head  of  Medusa.  Now 
Medusa  was  once  a  beautiful  maiden,  who  dared  to 
compare  her  ringlets  with  those  of  Minerva ;  where- 
upon the  goddess  changed  her  locks  into  hissing 
serpents,  and  made  her  features  so  hideous,  that  she 
turned  to  stone  every  living  object  upon  which  she 
fixed  her  Gorgon  gaze.  Perseus  was  at  first  quite 
overpowered  at  the  thought  of  undertaking  this  en- 
terprise, but  was  visited  by  Mercury,  who  promised 
to  be  his  guide,  and  to  furnish  him  with  his  winged 
shoes.  Minerva  loaned  him  her  wonderful  shield, 
that  was  bright  as  a  mirror.  The  Nymphs  gave  him, 
in  addition,  Pluto's  helmet,  which  made  the  bearer 
invisible.  Thus  equipped,  Perseus  mounted  into  the 
air  and  flew  to  the  ocean,  where  he  found  the  three 
Gorgons,  of  whom  Medusa  was  one,  asleep.  Fear- 
ing to  gaze  in  her  face,  he  looked  upon  the  image 
reflected  in  Minerva's  shield,  and  with  his  sword 
severed  Medusa's  head  from  her  body.  The  blood 
gushed  forth,  and  with  it  the  winged  steed  PEGASUS. 
Grasping  the  head,  Perseus  flew  away.  The  other 
Gorgons  awaking,  pursued  him,  but  he  escaped  their 
search  by  means  of  Pluto's  helmet.  Flying  over  the 
wilds  of  Libya,  in  his  aerial  route,  drops  dripping 


EQUATORIAL  CONSTELLATIONS.  245 

from  the  gory  head  of  the  monster  produced  the  in- 
numerable serpents  for  which  that  country  was  after- 
ward celebrated. 

Andromeda  is  represented  as  a  beautiful 
maiden  chained  to  a  rock. 

Principal  stars. — Algenib  and  Algol  in  Perseus? 
form,  with  Almaach  (7)  in  the  left  foot  of  Androme- 
da, a  right-angled  triangle  opening  toward  Cassio- 
peia. This  figure  is  so  perfect,  that  the  stars  may 
be  easily  recognized.  The  girdle  is  pointed  out  bj 
Merach  ((3),  and  two  other  stars  which  form  a  line 
slightly  curving  toward  the  right  foot.  The  breast  is 
denoted  by  a  very  delicate  triangle  composed  of 
three  stars,  8  of  the  fourth  magnitude,  another  of  the 
fifth  magnitude  just  south,  and  an  exceedingly  minute 
star  a  little  at  the  west.  Alpheratz  (a),  in  the  head 
of  Andromeda,  belongs  also  to  PEGASUS.  This  star, 
with  three  others,  all  of  the  second  magnitude,  con- 
stitute the  "  Great  Square  of  Pegasus."  Their  names 
are  Algenib  (y),  Markab  (a),  and  Scheat  (|3).  The 
brightest  stars  of  these  two  constellations  form  a 
figure  strikingly  like  the  Big  Dipper.  Algenib  and 
Alpheratz  lie  in  the  equinoctial  colure  which  passes 
through  Caph. 

.  Mythological  history. — Cassiopeia  had  boasted  that 
her  daughter  Andromeda  was  fairer  than  the  Sea- 
nymphs.  They  appealed,  in  great  indignation,  to 
Neptune,  who  sent  a  sea-monster  (CETUS)  to  devas- 
tate the  coast  of  Ethiopia.  To  appease  the  deities, 
her  father  Cepheus  was  directed  by  the  oracle  to 


246  THE   SIDEREAL  SYSTEM. 

bind  his  daughter  to  a  rock,  to  be  devoured  by  Cetus. 
Perseus  returning  from  the  destruction  of  Medusa, 
saw  Andromeda  in  her  forlorn  condition.  Struck  by 
her  beauty  and  tears,  he  offered  to  liberate  her 
at  the  price  of  her  hand.  Her  parents  consented 
joyfully,  and,  in  addition,  offered  a  royal  dowei. 
Perseus  slew  the  terrible  monster,  and  freeing  An- 
dromeda, restored  her  to  her  parents.  All  the  promi- 
nent actors  in  this  scene  were  honored  with  seats 
among  the  constellations.  The  Sea-nymphs,  it  is 
said,  in  petty  spite  of  Cassiopeia,  prevailed  that  she 
should  be  placed  where  for  half  of  the  time  she 
hangs  with  her  head  downward — a  fit  lesson  of  hu- 
mility. Cepheus,  her  husband,  shares  in  her  pun- 
ishment. 

Aries,  the  ram,  was  anciently  the  first  constella- 
tion of  the  zodiac.  It  is  now  the  first  sign,  but  the 
second  constellation.  On  account  of  the  precession  of 
the  equinoxes,  the  constellation  Pisces  occupies  the 
first  sign. 

Principal  stars. — The  most  noted  star  is  a  Arietis 
(Alpha  of  Aries,  more  commonly  called  simply  Arie- 
tis), in  the  right  horn.  This  lies  near  the  path  of  the 
moon  and  is  one  of  the  stars  from  which  longitude  is 
reckoned.  A  line  drawn  from  Almaach  to  Arietis 
will  pass  through  a  beautiful  figure  of  three  stars 
called  the  THE  TRIANGLES. 

Mythological  history. — Phryxus  and  Helle  were  the 
children  of  Athamas,  king  of  Thessaly.  Being  per- 
secuted by  Ino,  their  step-mother,  they  were  com- 


EQUATORIAL  CONSTELLATIONS.  247 

pelled  to  flee  for  safety.  Mercury  provided  them  a 
rani  which  bore  a  golden  fleece.  The  children  were 
no  sooner  placed  on  his  back  than  he  vaulted  into 
the  heavens.  In  their  aerial  journey  Helle  becom- 
ing dizzy  fell  off  into  the  sea,  which  was  afterward 
called  the  Hellespont,  now  the  Dardanelles.  Phryx- 
us  coming  in  safety  to  Colchis,  on  the  eastern  shore 
of  the  Black  Sea,  offered  the  ram  in  sacrifice  to  Ju- 
piter, and  gave  the  golden  fleece  to  Aetes,  his  pro- 
tector. The  Argonautic  expedition  in  pursuit  of  this 
golden  fleece,  by  Jason  and  his  followers,  is  one  of 
the  most  romantic  of  mythological  stories.  It  is, 
undoubtedly,  a  fanciful  account  of  the  first  impor- 
tant maritime  expedition.  Rich  spoils  were  the 
prizes  to  be  secured. 

Taurus  consists  only  of  the  head  and  shoulders 
of  a  lull,  which  is  represented  im  the  act  of  plunging 
at  Orion. 

Principal  stars. — The  Hyades,  a  beautiful  cluster 
in  the  head,  forms  a  distinct  Y.  TJhe  brightest  of 
these  is  Aldebaran,  a  fiery  red  star  of  the  first  mag- 
nitude. The  Pleiades*  or  the  "  Seven  Sisters,"  as 
it  is  sometimes  termed,  is  the  most  conspicuous 
group  in  the  heavens.  It  contains  a  large*  number  of 
stars,  six  of  which  are  visible  to  the  naked  eye. 
There  were  said  to  have  been  anciently  seven,  but 
Electra  left  her  place  that  she  might  not  behold  the 
ruin  of  Troy,  which  was  founded  by  her  son  Dar- 

*  Job.  xxxyiii.  31 ;  Amos,  v.  8. 


;448  THE   SIDEREAL   SYSTEM. 

danus.  Others  say  that  the  "  lost  Pleiad"  was  Mero- 
pe,  who  married  a  mortal.  Alcyone  is  the  most  dis- 
tinctly seen.  El  Nath  (#)  and  £  point  out  the  horns 
of  Taurus. 

Mythological  history. — This  is  the  animal  whose 
form  Jupiter  assumed  when  he  bore  off  Europa.  The 
Pleiades  were  the  daughters  of  Atlas,  arid  Nymphs 
of  Diana's  train.  They  were  distinguished  for  their 
unblemished  virtue  and  mutual  affection.  The  hunt- 
er OnioN  having  pursued  them  one  day,  they  prayed 
to  the  gods  in  their  distress.  Jupiter  in  pity  trans- 
ferred them  to  the  heavens. 

A.uvi(/ci,  the  Charioteer  or  Wagoner,  is  represented 
as  a  man  resting  one  foot  on  a  horn  of  Taurus,  and 
holding  a  goat  and  kids  in  his  left  hand  and  a  bridle 
in  his  right. 

The  principal  stars  are  arranged  in  an  irregular 
five-sided  figure,  which  is  very  noticeable.  Capella, 
the  goat-star,  is  of  the  first  magnitude.  It  travels 
in  its  orbit  1,800  miles  per  minute;  and  it  takes 
seventy-two  years,  or  a  man's  lifetime,  for  its  light 
to  reach  the  earth.  Near  by  is  a  delicate  triangle 
formed  of  three  small  stars,  called  tlte  Kids.  Men- 
kalini  (/3)  is  in  the  right  shoulder,  6  in  the  right 
hand,  /3  (common  to  Auriga  and  Taurus)  the  right 
foot  and  t>  the  left  foot.  Capella,  /3?>  and  «?  (a  star  in 
the  head)  form  a  triangle.  The  origin  of  this  con- 
stellation is  unknown. 

Pisces,  the  fakes,  is  represented  by  two  fishes 
tied  together  by  a  long  ribbon.  It  consists  of  small 


EQUATORIAL  CONSTELLATIONS. 


249 


stars,  which  can  be  traced  only  upon  a  cle/ir  night, 
and  in  the  absence  of  the  moon. 

Cetus,  the  wJiale,  is  a  huge  sea-monster,  slowly 
ploughing  his  way  westward,  midway  between  the 
horizon  and  the  zenith.  It  may  easily  be  found,  on 
a  clear  night,  by  means  of  the  numerous  figures 
given  in  the  map. 

(Map  No.  3)— Fig.  75. 


Gemini,  the  Twins  t  represents  the  twin  brothers 
Castor  and  Pollux. 

The  principal  stars  are  Castor  and  Pollux,  which 
are  of  the  first  and  second  magnitudes.  The  latter 
is  also  one  of  the  stars  from  which  longitude  is  reck- 
oned by  means  of  the  Nautical  Almanac.  The  con- 
stellation is  clearly  distinguished  by  means  of  two 
nearly  parallel  rows  of  stars,  which  by  a  slight  effort 

It* 


250  THE   SIDEKEAL   SYSTEM. 

of  the  imagination  may  be  extended  into  the  constel- 
lations Taurus  and  Orion. 

Mythological  history. — Castor  and  Pollux  were  no- 
ted— the  former  for  his  skill  in  training  horses,  the 
latter  for  boxing.  They  were  tenderly  attached  to 
each .  other,  and  were  inseparable  in  all  their  adven- 
tures. They  accompanied  Jason  on  the  Argonautic 
expedition.  A  storm  having  arisen  on  this  voyage, 
Orpheus  played  on  his  wonderful  lyre  and  prayed  to 
the  gods ;  whereupon  the  tempest  was  stilled,  and 
star-like  flames  shone  upon  the  heads  of  the  twin- 
brothers.  Sailors,  therefore,  considered  them  as  pa- 
tron deities,*  and  the  balls  of  electric  flame  seen  on 
masts  and  shrouds,  now  called  St.  Elmo's  fire,  were 
named  after  them.  Afterward,  Castor  was  slain. 
Pollux  being  inconsolable,  Jupiter  offered  to  take 
him  up  to  Olympus,  or  to  let  him  share  his  immor- 
tality with  his  brother.  Pollux  preferred  the  latter, 
and  so  the  brothers  pass  alternately  one  day  under 
the  earth,  and  the  next  in  the  Elysian  Fields.  Not 
only  did  sailors  thus  think  them  to  watch  over  navi- 
gation, but  they  were  believed  to  return,  mounted  on 
snow-white  steeds  and  clad  in  rare  armor,  to  take 
part  in  the  hard-fought  battle-fields  of  the  Komans. 


"  Back  comes  the  chief  in  triumph, 
Who  in  the  hour  of  fight 
Hath  seen  the  great  Twin  Brethren, 
In  harness  on  his  right. 


Acts,     xxviii.  11. 


EQUATORIAL  CONSTELLATIONS.  251 

Safe  comes  the  ship  to  haveii. 

Through  billows  and  through  gales, 
If  once  the  great  Twin  Brethren 

Sit  shining  on  the  sails.'1— Lays  of  Ancient  Home. 

Orion  is  represented  under  the  figure  of  a  hunter 
assaulting  Taurus.  He  has  a  sword  in  his  belt,  a 
club  in  his  right  hand,  and  the  skin  of  a  lion  in  his 
left.  This  is  one  of  the  most  clearly  defined  and 
conspicuous  constellations  in  the  heavens. 

Principal  stars. — Four  brilliant  stars,  in  the  form  of 
a  parallelogram,  mark  the  outlines  of  Orion.  Betel- 
geuse,  a  beautiful  ruddy  star  of  the  first  magnitude, 
is  in  the  right  shoulder ;  Bellatrix  (7),  of  the  second 
magnitude,  is  in  the  left  shoulder ;  Eigel,  of  the  first 
magnitude,  is  in  the  left  foot ;  and  Saiph  (x),  of  the 
third  magnitude,  is  in  the  right  knee.  Two  small 
stars  near  X  form  with  it  a  small  triangle,  which  is 
itself  the  vertex  of  a  larger  triangle  composed  of  \ 
y,  and  Betelgeuse.  Near  the  centre  of  the  parallel- 
ogram are  three  stars  forming  " the  Belt  of  Orion" 
called  also  the  "  Bands  of  Orion"  (Job,  xxxviii.  31), 
Jacob's  rod.  but  more  commonly  the  "  Ell  and  Yard." 
They  received  the  last  name  because  they  form  a 
line  just  3°  long,  divided  in  equal  parts  by  a  star 
in  the  centre.  These  divisions  are  useful  for  meas- 
uring the  distances  of  the  stars.  Kunning  from  the 
belt  southward,  is  an  irregular  line  of  stars  which 
marks  the  sword  ;  and  west  of  Bellatrix  is  a  curved 
line  denoting  the  lion's  skin.  South  of  Orion  are  four 
stars  forming  a  beautiful  figure  styled  the  HARE. 


252  THE   SIDEREAL  SYSTEM. 

Mythological  History. — Orion  was  a  famous  hunter. 
Becoming  enamored  of  Merope,  he  desired  to  mar- 
ry her.  (Enopion,  her  father,  opposing  the  choice, 
took  a  favorable  opportunity  and  put  out  the  eyes  of 
the  unwelcome  suitor.  The  blinded  hero  followed 
the  sound  of  a  Cy clop's  hammer  until  he  came  to  Vul- 
can's forge.  He,  taking  pity,  instructed  Kedalion  to 
conduct  him  to  the  abode  of  the  sun.  Placing  his 
guide  on  his  shoulder,  Orion  proceeded  to  the  east, 
and  at  a  favorable  place 

"  Climbing  up  a  narrow  gorge, 
Fixed  his  blank  eyes  upon  the  sun." 

The  healing  beams  restored  him  to  sight.  As  a  pun- 
ishment for  having  profanely  bpasted  that  he  was 
able  to  conquer  any  animal  the  earth  could  produce, 
he  was  bitten  in  the  heel  by  a  scorpion.  Afterward, 
Diana  placed  him  among  the  stars ;  where  SIRIUS 
and  PROCYON,  his  dogs,  follow  him,  the  PLEIADES  fly 
before  him,  and  far  remote  is  the  SCORPION,  by  whose 
bite  he  perished. 

Canis  Major  and  Cants  Minor  contain  each  a 
single  star  of  the  first  magnitude,  Sirius  and  Procyon. 
These  two,  with  Betelgeuse,  Phaet  in  the  Dove,  and 
Naos  in  the  Ship,  form  a  huge  figure  known  as 
the  Egyptian  X.  Sirius,  the  dog-star,  is  the  most 
brilliant  star  in  the  heavens.  It  travels  at  the  rate 
of  840  miles  per  minute.  Twenty-two  years  are 
required  for  its  light  to  reach  the  earth  ;  its  distance 
being  estimated  at  1,375,000  times  that  of  the  sun 
from  us.  1!  :ts  intrinsic  brilliancy  be  the  same  as 


EQUATORIAL   CONSTELLATIONS.  253 

that  of  our  sun,  its  diameter  at  that  distance  must  be 
fifteen  times  as  great,  or  12,000,000  miles.  Prob- 
ably these  estimates  fall  far  below  the  reality  of  this 
magnificent  orb. 

(Map  No.  4)-  Fi#.  76. 


Leo  is  represented  as  a  rampant  lion.  It  is  one  of 
the  most  beautiful  constellations  in  the  zodiac. 

The  principal  stars  are  arranged  in  the  form  of  a 
sickle.  Kegulus,  in  the  handle,  is  a  brilliant  star  of 
the  first  magnitude.  It  is  one  of  the  stars  from  which 
longitude  is  reckoned.  It  is  almost  exactly  in  the 
ecliptic.  Zosma  (5)  lies  in  the  back  of  the  lion,  £  in 


254  THE   SIDEREAL  SYSTEM. 

the  thigh,  and  Denebola,  a  star  of  the  second  mag- 
nitude, in  the  brush  of  the  tail. 

Cancer  includes  the  stars  which  lie  irregularly 
scattered  between  Gemini,  Head  of  Hydra,  Procyon, 
and  Leo.  In  the  midst  of  these  is  a  luminous  spot, 
called  Presepe  or  the  Beehive,  which  an  ordinary 
glass  will  resolve  into  stars. 

Virgo  is  represented  as  a  beautiful  maiden  with 
folded  wings,  bearing  in  her  left  hand  an  ear  of 
corn. 

The  principal  star  is  Spica  Virginis,  in  the  ear  of 
corn.  It  is  of  the  first  magnitude,  and  is  used  for 
determining  longitude  at  sea.  Denebola,  Cor  Caroli, 
(a),  Arcturus  (Map  No.  5),  and  Spica  form  a  figure 
about  50°  in  length  from  north  to  south,  called  the 
Diamond  of  Virgo.  The  other  stars  may  be  easily 
traced  by  means  of  the  map. 

Mythological  History. — Virgo  was  the  goddess  As- 
trsea.  According  to  the  poets,  the  early  history  of 
man  was  the  golden  age.  It  was  a  time  of  inno- 
cence and  truth.  The  gods  dwelt  among  men,  and 
perpetual  Spring  delighted  the  earth.  Next  came 
the  silver  age,  less  tranquil  and  serene,  but  still  the 
gods  lingered  and  happiness  prevailed.  Then  fol- 
lowed the  brazen  and  iron  ages,  when  wickedness 
reigned  supreme.  The  earth  was  wet  with  slaughter 
The  gods  left  the  abodes  of  men  one  by  one,  As- 
trnea  alone  remaining ;  until  finally  she  too,  last  of  all 
the  immortals,  bade  the  earth  farewell.  Jupiter 
thereupon  placed  her  among  the  constellations. 


EQUATORIAL  CONSTELLATIONS.  255 

Hydra  is  a  long  straggling  serpent  having  its  head 
near  Procyon  and  extending  its  tail  beyond  Virgo, 
a  total  distance  of  more  than  100°. 

The  principal  star  is  Cor  Hydrae,  of  the  second 
magnitude.  It  is  a  lone  star,  and  may  be  easily  found 
by  a  line  drawn  from  y  Leonis  through  Regulus, 
and  continued  about  23°.  The  head  is  marked  by  a 
rhomboidal  figure  of  four  stars  of  the  fourth  magni- 
tude lying  near  Procyon.  Several  delicate  triangles 
may  be  formed  of  them  and  other  small  stars  lying 
near.  The  Crater  or  Cup  is  a  beautiful  and  very 
striking  semicircle  of  six  stars  of  the  fourth  magni- 
tude directly  south  of  6  Leonis.  Corvus,  the  raven, 
lios  15°  east  of  the  Cup.  e  Corvi  is  in  the  equinoctial 
colure. 

Mythological  history. — Hydra  was  a  fearful  serpent 
which  in  ancient  times  infested  the  lake  Lerna.  Its 
destruction  constituted  one  of  the  twelve  labors  of 
Hercules.  The  Crow  was  formerly  white,  it  is  said, 
but  was  changed  to  its  raven  tint  on  account  of  its 
proneness  to  tale-bearing. 

Cor  Caroli  (a)  is  marked  by  a  line  passing  from 
Benetnasch  (*])  through  Berenice's  Hair  to  Denebola 

W). 

Berenice's  Hair  is  a  beautiful  cluster  midway 
between  Cor  Caroli  and  Denebola.  Nearby  is  a  single 
bright  star  of  the  fourth  magnitude. 

Mythological  history. — Berenice  was  the  wife  of 
Ptolemy.  Her  husband  going  upon  a  dangerous  ex- 
pedition, she  promised  to  consecrate  her  beautiful 


256 


THE   SIDEREAL   SYSTEM. 


tresses  to  Venus  if  he  should  return  in  safety.  Soon 
after  the  fulfilment  of  this  vow  the  hair  disappeared 
from  the  temple  where  it  had  been  deposited 
Berenice  being  much  disquieted  at  this  loss,  Conon, 
the  astronomer,  announced  that  the  locks  had  been 
transferred  to  the  heavens.  In  proof  of  which,  he 
pointed  out  this  cluster  of  hitherto  unnamed  stars. 
All  parties  were  satisfied  with  this  happy  termina- 
tion of  the  difficulty. 

(Map  No.  5)-Fig.  77. 


Bootes,  the  bear-driver,  is  represented  as  a  hunts- 
man grasping  a  club  in  his  right  hand,  while  in  his 
left  he  holds  by  the  leash  his  two  greyhounds,  with 
which  he  is  pursuing  the  Great  Bear  continually 
around  the  north  pole. 

Principal   stars. — Arctnrua,*    a   magnificent   star 

*  Job,  ix.  9. 


EQUATORIAL   CONSTELLATIONS.  257 

of  the  first  magnitude,  is  in  the  left  knee.  It  forms 
a  triangle  with  Denebola  and  Spica,  and  also  one 
with.  Denebola  and  Cor  Caroli.  It  travels  in  its  orbit 
fifty-four  miles  per  second,  or  more  than  three  times 
as  fast  as  the  earth.  Its  light  reaches  the  earth  in 
about  twenty-six  years.  Mirac  (s)  lies  in  tlje  girdle, 
S  in  the  right  shoulder,  Alkaturops  (M-)  in  the  club,  /3 
in  the  head,  and  Seginus  (y)  in  the  left  shoulder. 
Seginus  forms  with  Oor  Caroli  and  Arcturus  a  tri- 
angle, right-angled  at  Seginus.  Three  small  stars 
in  the  left  hand  of  Bootes  lie  near  Benetnasch. 

Mythological  history. — Bootes  is  supposed  to  have 
been  Areas,  the  son  of  Callisto.  (See  Ursa  Major.) 

Hercules  is  represented  as  a  warrior  clad  in  the 
skin  of  the  Nemsean  lion,  holding  a  club  in  his  right 
hand  and  the  dog  Cerberus  in  his  left.  His  foot  is 
near  the  head  of  Draco,  while  his  head  lies  38°  south, 
and  his  club  reaches  10  degrees  beyond. 

The  principal  star  is  Has  Algethi  («•  of  Hercules 
and  %  of  Serpentarius).  This  forms  a  triangle  with 
|3  and  S.  A  peculiar  figure  of  four  stars  (*,  nj,  £,  e), 
north  of  these,  marks  the  body.  (See  Maps,  Nos. 
5,  7,  and  7.)  The  left  knee  is  pointed  out  by  6,  and 
the  left  foot  by  y. 

Mythological  history. — This  constellation  immor- 
talizes the  name  of  one  of  the  greatest  heroes  of 
antiquity.  Hercules  was  the  son  of  Jupiter  and 
Alcmena.  While  he  was  yet  lying  in  his  cradle, 
Juno,  in  her  jealousy,  sent  two  serpents  to  destroy 
him.  The  precocious  infant,  however,  strangled 


258  THE    SIDEREAL   SYSTEM. 

them  with  his  hands.  By  the  canning  artifice  of 
Juno,  Hercules  was  made  subject  to  Eurystheus,  his 
elder  half-brother,  and  compelled  to  perform  all  his 
commands.  Eurystheus  enjoined  upon  him  a  series 
of  the  most  difficult  and  dangerous  enterprises  which 
could  be  conceived.  These  are  termed  the  "  Twelve 
Labors  of  Hercules."  Having  completed  these 
tasks,  he  afterward  achieved  others  equally  cele- 
brated. Near  the  close  of  his  life  he  killed  the  cen- 
taur Nessus.  The  dying  monster  charged  Dejanira, 
the  wife  of  Hercules,  to  preserve  a  portion  of  his 
blood  as  a  charm  to  use  in  case  the  love  of  her  hus- 
band should  ever  fail  her.  In  time,  Dejanira  thought 
she  needed  the  potion,  and  Hercules  having  sent  for 
a  white  robe  to  wear  at  a  sacrifice,  she  steeped  the 
garment  in  the  blood  of  Nessus.  No  sooner  had 
Hercules  put  on  the  fatal  robe  than  the  venom  stung 
his  bones  and  boiled  through  his  veins.  He  at- 
tempted to  tear  it  off,  but  in  vain.  It  stuck  to  his 
flesh,  and  tore  off  great  pieces  of  his  body.  The 
hero  finding  he  must  die,  ascended  Mount  (Eta, 
where  he  erected  a  funeral  pyre,  spread  out  the  skin 
of  the  Nema3an  lion,  and  laid  himself  down  upon 
it.  Philoctetes  applied  the  torch.  With  perfect  se- 
renity of  countenance  Hercules  awaited  approaching 
death — 

"  Till  the  god,  the  earthly  part  forsaken, 
From  the  man  in  flames  asunder  taken, 
Drank  the  heavenly  ether's  purer  breath. 
Joyous  in  the  new  unwonted  lightness 
•  Soared  he  upward  to  celestial  brightness, 

Earth's  dark,  heavy  burden  lost  in  death." 

SCHILLER. 


EQUATORIAL   CONSTELLATIONS. 
(Map  No.  6)— Fig.  78. 


259 


Corona  consists  of  six  stars  arranged  in  a  semi- 
circular form.  The  brightest  of  these  is  Alphacca. 
This  makes  a  triangle,  with  Mirac  (e)  and  d  in  Bootes. 
It  forms  a  similar  figure  with  Mirac  and  Arcturus. 

Serpentarius,  or  Ophiuchus,  the  serpent- 
bearer,  is  represented  under  the  figure  of  a  man 
grasping  in  both  hands  a  prodigious  serpent,  which 
is  writhing  in  his  grasp. 

Principal  stars. — Eas  Alhague  (a),  in  the  head,  is 
of  the  second  magnitude.  It  is  about  5°  from  Eas 
Algethi.  They  form  a  pair  of  stars  conspicuous  like 
the  pairs  in  Gemini,  Canis  Minor,  Canis  Major,  etc. 
Q  marks  the  right  shoulder,  and  x  the  left.  There  is 


260  THE   SIDEREAL   SYSTEM. 

a  small  cluster  near  ft,  called  TAUEUS  PONIATOWSKII. 
An  irregular  square  of  four  stars,  near  /  Herculis, 
denotes  the  head  of  the  serpent. 

Mythological  history. — This  constellation  perpetu- 
ates the  memory  of  2Esculapius,  the  father  of  medi- 
cine. He  was  so  skilful  that  he  restored  several  to 
life;  whereupon  Pluto  complained  to  Jupiter  that 
his  kingdom  was  in  danger  of  being  depopulated. 
Therefore  Jupiter  struck  him  with  a  thunderbolt, 
but  afterward  placed  him  among  the  constellations. 
Serpents  were  sacred  to  .ZEsculapius,  because  of  the 
superstitious  idea  that  they  have  the  power  of  re- 
newing their  youth  by  changing  their  skin. 

Libra  represents  the  scales  of  Astraea  (Virgo),  the 
goddess  of  justice.  It  may  be  recognized  by  the 
quadrilateral  figure  formed  by  its  four  principal 
stars. 

Scorpio  is  represented  under  the  figure  of  a  huge 
scorpion,  stretching  through  25°.  It  is  a  most  in- 
teresting constellation. 

Principal  stars. — Antares  (a)  is  a  fiery  red  star  of  the 
first  magnitude.  It  marks  the  heart  of  the  Scor- 
pion. The  head  is  indicated  by  several  stars,  the 
most  prominent  of  which  is  /3,  arranged  in  a  line 
slightly  curved.  The  tail  may  be  easily  traced  by  a 
series  of  stars  which  wind  around  through  the 
Milky  Way  in  a  very  beautiful  manner. 

Mythological  history. — This  is  the  scorpion  that 
sprang  out  of  the  earth  at  the  command  of  Juno, 
and  stung  Orion.  Scorpio  and  Orion  are  so  placed 


EQUATORIAL  CONSTELLATIONS.  261 

among  the  constellations  that  they  never  appear  in 
the  heavens  together. 

Sagittarius,  the  archer,  is  represented  as  a  cen- 
taur with  his  bow  bent,  as  if  about  to  let  fly  an 
arrow  at  Scorpio. 

Principal  stars. — A  row  of  stars  from  /x  to  (3  marks 
the  bow :  another  from  7  eastward  points  out  the 
arrow  and  the  right  arm  drawn  back  in  bending  the 
bow.  North  of  r,  two  stars  of  the  fourth  magnitude 
denote  the  head  of  the  centaur.  The  "  Milk  Dipper" 
so  called  because  the  handle  lies  in  the  Milky  Way, 
is  a  very  striking  figure. 

Mythological  history. — This  constellation  is  named 
in  honor  of  Chiron,  one  of  the  centaurs.  These 
monsters  were  represented  as  men  from  the  head  to, 
the  loins,  while  the  remainder  of  the  body  was  that 
of  a  horse — of  which  animal  the  ancients  had  so  high 
an  opinion  that  this  union  was  not  considered  in  the 
least  degrading.  Chiron  was  renowned  for  his  skill 
in  music,  medicine,  hunting,  and  the  art  of  prophecy. 
The  most  distinguished  heroes  of  mythology  were 
among  his  pupils.  He  taught  2Esculapius  physic, 
ApoUo  music,  and  Hercules  astronomy.  At  his 
death,  the  centaur  furnished  Dejanira  with  the  in- 
formation which  proved  so  fatal  to  Hercules. 

Capricornus  contains  no  very  conspicuous  stars. 
The  SOUTHERN  FISH  (No.  6)  has  one  star  of  the  first 
magnitude,  Fomalhaut  (a,  No.  7),  which  on  a  clear 
summer  evening  may  be  seen  in  the  south  mid- 
way to  the  zenith.  ANTINOUS  AND  THE  EAGLE  is  a 


262 


THE   SIDEREAL   SYSTEM. 


double  constellation.  It  contains  a  beautiful  star 
of  the  first  magnitude,  Altair.  This  is  conspicuous, 
as  being  the  centre  one  in  a  row  of  three  bright  stars. 
A  similar  row,  the  first  star  of  which  is  named  '(,  de- 
notes the  tail  of  the  eagle,  the  last  star  lying  in  Cerberus. 
The  DOLPHIN  is  a  beautiful  little  cluster  in  the  form 
of  a  diamond.  It  is  sojnetimes  called  "  Job's  Coffin." 

(Map  No.  7)— Fig.  79. 


Cygnus,  the  swan,  is  a  remarkable  group  of  stars, 
the  principal  ones  being  so  arranged  as  to  form  a 
large  and  beautiful  cross.  The  upright  piece  lies 
along  the  Milky  Way.  It  is  composed  of  four  stars, 
three  of  which,  Deneb  (a),  7,  and  /3,  are  bright,  while 
the  fourth  is  a  variable  star.  In  this  constellation, 
No.  61,  a  minute  star,  scarcely  visible  to  the  naked 
eye,  is  noted  as  being  the  nearest  to  the  earth  i  f  any 
of  the  fixed  stars  in  the  northern  hemisphere. 


THE   SOUTHERN   CONSTELLATIONS. 


263 


Lyra,  the  harp,  contains  one  brilliant  blue  star, 
Vega.  Close  by  it  is  a  parallelogram  of  four  smaller 
stars,  by  which  it  may  be  easily  recognized.  This  is 
the  celestial  lyre  upon  which  Orpheus  discoursed 
such  ravishing  music  that  wild  beasts  forgot  their 
fierceness  and  gathered  about  him  to  listen,  while 
the  rivers  ceased  to  flow,  and  the  very  rocks  and 
trees  stood  entranced. 


THE  SOUTHEKN  CONSTELLATIONS 

fMao  No.  8)— Fte.  80. 


We  now  imagine  ourselves  viewing  the  stars  visible 
only  to  a  person  south  of  the  equator.  The  constel- 
lations are  reversed  with  reference  to  the  horizon. 
The  two  stars  which,  in  the  northern  hemisphere. 


264 


THE   SIDEREAL   SYSTEM. 


compose  the  base  of  the  parallelogram  in  Orion, 
form  here  the  upper  side.  Sirius  is  above  Orion. 
All  the  northern  circumpolar  constellations  are 
hidden  from  view.  At  the  southern  pole  there  is  no 
conspicuous  star,  but  the  richness  and  number  of 
the  neighboring  stars  compensate  this  deficiency, 
and  give  to  the  heavens  an  incomparable  splendor. 
Here  is  the  magnificent  constellation  Argo,  in  which 
we  find  Canopus,  looked  upon  in  ancient  times  as 

(Map  No.  9)— Fig.  81. 


next  to  Sirius  in  brilliancy :  ?j,  a  variable  star,  now 
surpasses  it  in  brightness. 

Nearly  at  the  height  of  the  south  pole  blazes  the 
SOUTHERN  CROSS  ;  below  is  the  CENTAUR,  containing 
two  stars  of  the  first  magnitude  and  five  of  the 
second ;  and  above  is  Hydrus,  where  shines  Achernar, 
anoiher  beautiful  star  of  the  first  magnitude. 


DOUBLE  STABS.  265 

DOUBLE  STAES,  COLOEED  STAES, 
NEBULAE,  ETC. 

DOUBLE  STAHS. — To  the  naked  eye  all  the  stars 
appear  single.  With  the  telescope,  over  6,000  have 
been  found  to  be  double.  Thus,  Polaris  consists  of 
two  stars  about  18"  apart,  Eigel  has  a  companion 
about  10"  from  it,  and  Sirias  one  distant  7".  A  good 
opera-glass  will  separate  s  Lyrse  into  two  compo- 
nents. In  case  two  stars  happen  to  He  in  the  same 
straight  line  from  us,  though  at  immense  distances 
from  each  other,  their  light  will  blend.  They  will  be 
seen  by  the  naked  eye  as  a  single  star,  and  by  the 
telescope  as  a  double  star.  They  are  called  optical 
double  stars.  Over  650,  however,  of  the  double  stars 
have  been  found  to  be  physically  connected.  Each 
double  star  of  this  class  forms  a  binary  system  of  two 
suns  revolving  in  an  elliptical  orbit  about  their  com- 
mon centre  of  gravity,  like  the  planets  in  the  solar  sys- 
tem, in  accordance  with  Newton's  law  of  gravitation. 
In  a  few  instances  there  are  combinations  of  triple, 
quadruple,  and  even  septuple  stars.  Thus  e  Lyrse  is  a 
double-double  star,  while  6  Orionis  is  a  system  of  seven 
suns.  The  components  of  a  double  star  commonly  dif- 
fer in  brightness  ;  so  that  frequently  the  fainter  one 
is  nearly  lost  in  the  brilliancy  of  its  companion  sun. 

The  periods  of  some  of  these  systems  have  been 
ascertained.  Thus,  |  Ursse  is  a  double  star,  and  the 
two  stars  of  which  it  is  composed  have  performed 
an  entire  revolution  about  each  other  sinoe  they  were 

H 


266  THE   SIDEREAL   SYSTEM. 

known  to  be  connected.  There  are  only  eight 
binary  stars  whose  periods  are  less  than  a  century, 
while  325  have  periods  which  seem  to  extend  one 
thousand  years. 

Orlits. — It  is  not  possible  to  estimate  the  dimen- 
sions of  the  orbits  of  the  double  stars,  until  their  dis- 
tances from  us  are  known.  Taking  the  estimated  dis- 
tance of  61  Cygni  (550,000  times  the  sun's  mean  distance 
from  the  earth)  as  a  basis,  the  companions  of  that 
system  cannot  cultivate  a  very  intimate  acquaintance, 
since  they  must  be  over  a  billion  miles  apart.  From 
these  data,  astronomers  have  even  attempted  to  cal- 
culate the  mass  of  some  of  the  double  stars.  61 
Cygni,  although  scarcely  visible  to  the  naked  eye, 
and  known  to  be  the  second  nearest  to  us  of  any  of 
the  fixed  stars,  is  yet  estimated  to  weigh  one-third 
as  much  as  our  sun. 

COLORED  STARS. — We  have  already  noticed  that  the 
stars  are  of  various  colors.  Sirius  is  white,  Antares 
red,  and  Capella  yellow ;  while  Lyra  has  a  blue  tint, 
and  Castor  a  green  one.  In  the  pure  transparent  at- 
mosphere of  tropical  regions,  the  colors  are  far  more 
brilliant.  There,  oftentimes,  the  nocturnal  sky  is  a 
blaze  of  jewels, — the  stars  glittering  with  the  green 
of  the  emerald,  the  blue  of  the  amethyst,  and  the  red 
of  the  topaz.  In  our  latitudes,  there  are  no  stars 
visible  to  the  naked  eye  which  are  decidedly  blue  or 
green.  In  the  double  and  multiple  stars,  every 
color  is  presented  in  all  its  richness  and  beauty. 
We  find  also  combinations  of  colors  complementary 
to  each  other.  Here  is  a  green  star  with  a  blood- 


VAKIABLE  STABS.  267 

red  companion :  here  an  orange  and  blue  sun-  there 
a  yellow  and  purple  one.  The  triple  star  y  Andro- 
medse,  is  formed  of  an  orange-red  sun  and  two  others 
of  an  emerald  green.  Every  tint  that  blooms  in  the 
flowers  of  summer,  flames  out  in  the  stars  at  night. 
"  The  rainbow  flowers  of  the  footstool  and  the  starry 
flowers  of  the  throne,"  proclaim  their  common 
Author ;  while  rainbow,  flower,  and  star  alike  evince 
the  same  Divine  love  of  the  beautiful. 

As  to  the  effects  produced  in  a  system  having  col- 
ored suns  we  can  hardly  conceive.  Take  a  planet  re- 
volving about  4*  Cassiopeise  for  instance.  This  is  il- 
luminated by  a  red,  a  blue,  and  a  green  sun.  Some- 
times, by  the  succession  of  these  suns,  a  cheerful 
green  day  would  present  a  charming  relief  to  a 
fiery  red  one ;  and  that  might  be  still  farther  sub- 
dued by  a  gentle  blue  one.  The  odd  contrasts  of 
color  and  the  vicissitudes  of  extreme  heat  and  cold 
which  obtain  on  such  a  world,  present  a  picture 
which  our  fancy  can  sketch  better  than  words  can 
paint.  The  colors  of  the  stars  change.  Sirius  was 
anciently  red.  It  is  now  unmistakably  white. 
There  are  two  double  stars  which  were  described  by 
Herschel  as  white  ;  they  are  each  now  composed  of 
a  golden-yellow  and  a  greenish  star. 

VARIABLE  STAKS. — These  are  stars  which  have  pe- 
riodic changes  of  brilliancy.  There  are  many  of  this 
class,  of  which  the  following  are  most  conspicuous. 
ALGOL,  in  the  head  of  Medusa,  is  a  star  of  the  second 
magnitude  for  about  two  and  a  half  days,  when  it 
suddenly  decreases,  and  in  three  and  a  half  hours 


268  THE  SIDEREAL  SYSTEM. 

descends  to  the  fourth  magnitude.  It  then  rekindles, 
and  in  three  and  a  half  hours  again  is  as  brilliant  aa 
ever.  MIRA,  the  ivonderful,  a  star  in  the  Whale,  has 
a  period  of  eleven  months.  Its  irregularities  are 
very  curious  and  fickle.  It  is  ordinarily  of  the 
second  magnitude  for  about  fifteen  days.  It  then 
decreases  for  three  months,  until  it  is  reduced  to 
the  9th  magnitude.  This  period  of  darkness  lasts 
five  months ;  it  then  rebrightens  for  three  months, 
until  it  regains  its  former  lustre.  Occasionally, 
however,  it  fails  to  brighten  at  all  beyond  the  fourth 
magnitude,  while  on  one  occasion  its  light  was 
almost  equal  to  that  of  Aldebaran.  Sometimes  no 
perceptible  change  takes  place  for  a  month ;  then 
again,  there  is  a  sensible  alteration  in  a  few  days. 

The  reason  of  this  variability  is  not  understood. 
It  has  been  suggested,  in  the  case  of  Mira,  that  it 
may  be  a  globe  revolving  on  its  axis,  and  that  dif- 
ferent portions  of  its  surface,  illuminated  to  different 
degrees  of  intensity,  are  thus  presented  to  us. 
Others  have  conceived  that  there  may  be  satellites 
revolving  about  these  suns,  and  that  when  their  dark 
bodies  interpose  between*  the  stars  and  our  earth, 
they  eclipse  their  light  wholly  or  in  part. 

TEMPORARY  STARS. — These  are  stars  which  sud- 
denly blaze  out  in  the  heavens,  and  then  gradually 
fade  away.  The  most  celebrated  one  of  this  class 
burst  forth  in  Cassiopeia,  in  the  year  1572.  Tycho 
Brahe  says :  "  One  night  as  I  was  examining  the  ce- 
lestial vault,  I  saw  with  unspeakable  astonishment  a 


TEMPORARY  STARS.  269 

star  of  extraordinary  brightness  in  Cassiopeia 
Struck  with  surprise,  I  could  scarcely  believe  my 
eyes.  To  convince  myself  that  there  was  no  illusion, 
I  called  the  workmen  of  my  laboratory  and  the 
passers-by,  and  asked  them  if  they  saw  the  star 
which  had  so  suddenly  made  its  appearance."  It  waa 
more  brilliant  than  Sirius  or  Jupiter  even,  and  could 
be  compared  only  with  Venus  at  her  quadrature,  ex- 
cept that  it  twinkled  wonderfully.  It  was  seen 
distinctly  at  midday.  Its  color  was  at  first  white, 
then  yellow,  and  finally  red.  Its  brightness  decreased 
gradually  until  the  spring  of  1574,  when  the  star  dis- 
appeared from  view  and  has  not  since  been  seen. 
As  two  brilliant  stars  had  previously  appeared  in 
Cassiopeia,  at  intervals  of  about  three  centuries, 
they  have  been  thought,  by  some,  to  be  identical, 
and  that  it  is  only  a  variable  star  of  long  period. 

Since  the  discovery  of  Tycho  Brahe,  numerous  in- 
stances are  recorded  of  stars  which  have  suddenly 
burst  forth,  and  then  either  faded  out  entirely,  or  re- 
mained only  as  faint  telescopic  objects.  In  the  latter 
case  they  are  termed  new  stars.  One  of  this  kind 
appeared  in  Corona  Borealis,  in  1866.  At  first  it  was 
of  the  second  magnitude,  but  in  a  week  changed  to 
the  fourth,  and  hi  a  month  diminished  to  the  9th. 
Strangely,  too,  some  stars  have  disappeared  from 
the  heavens,  and  are  styled  lost  stars.  These  changes 
which  are  thus  constantly  taking  place  are  calculated 
to  make  the  term  "  eternal  stars"  seem  a  very  in- 
definite phrase. 


270  THE   SIDEREAL  SYSTEM. 

Explanation. — These  phenomena  are  as  yet  little 
understood.  A  revolution  about  the  axis  would  fail 
to  explain  the  changes  in  color,  besides  being  in  it- 
self a  very  unaccountable  supposition.  Some  think 
that  these  stars  revolve  in  enormous  orbits  of  such 
eccentricity  that  at  their  most  distant  points  they 
fade  out  of  sight.  Arago  has  shown,  in  reply  to  this, 
that  for  a  star  to  decrease  in  brightness  from  the  first 
magnitude  to  the  second  by  simply  moving  directly 
from  us,  would  require  six  years,  even  if  it  should 
speed  away  with  the  velocity  of  light.  As  we  have 
just  seen,  the  star  of  1866  underwent  this  change  in 
brilliancy  in  a  week. 

The  mind  cannot  help  wondering  if  they  are  not 
instances  of  enormous  conflagrations  in  which  a 
world  is  overwhelmed  in  ruin !  The  investigations 
of  spectrum  analysis  indicate  that  the  star  of  1866 
consisted  of  burning  hydrogen  gas.  We  can  suppose 
that  this  was  evolved  by  some  convulsion,  and  taking 
fire,  wrapped  in  flames  the  entire  globe.  This  need 
not  involve  the  idea  of  destruction,  but  only  a  change 
of  form.  In  this  manner  a  dark  star  may  become 
luminous,  or  a  bright  one  may  be  extinguished. 

Thus  do  we  see  that  the  process  of  apparent  crea- 
tion and  destruction  is  going  on  in  the  heavens  imme- 
diately before  the  eye  of  the  astronomer.  New 
stars  flash  into  light,  old  stars  are  lost,  worlds  burst 
into  flame,  and  their  glowing  embers  fade  into  dark- 
ness. Are  they  re-created  into  new  worlds?  We 
know  not.  We  only  perceive  that  the  same  Al- 


STAR  CLUSTERS.  271 

mighty  power  which  fitted  up  this  earth  for  our 
home  is  yet  at  work  among  the  worlds  about  us,  and 
we  are  thus  witnesses  of  His  eternal  presence. 

STAR  CLUSTERS. — These  are  groups  of  stars  so 
massed  together  as  to  present  a  hazy,  cloud-like  ap- 
pearance. Several  of  them  have  been  already 
named — the  Pleiades,  the  Beehive  in  Cancer,  Bere- 
nice's Hair,  the  Hyades,  and  the  group  in  the  sword- 
handle  of  Perseus.  The  stars  of  which  they  are 
composed  can  generally  be  easily  distinguished  by 

Fig.  82. 


STAR-CLUSTER  IN  TOUCAN. 


the  naked  eye,  although  by  the  use  of  a  small  opera 
or  spy  glass  the  number  is  largely  increased.  In 
the  southern  sky  there  are  clusters  still  more  re- 
markable. In  the  Cross  is  a  group  of  110  stars  of 


272  THE  SIDEREAL  SYSTEM. 

various  colors,  red,  blue,  and  green,  so  that  looking 
on  it,  says  Herschel,  is  "like  gazing  into  a  casket 
of  precious  gems."  A  cluster  in  Toucan  is  compact  at 
the  centre,  where  it  is  of  an  orange-red  color ;  the 
exterior  is  composed  of  pure  white  stars,  making  a 
border  of  exquisite  contrast.  It  is  generally  conceded 
that  there  is  some  close  physical  relation  existing 
between  the  stars  composing  such  an  "  archipelago  of 
worlds,"  but  its  nature  is  a  mystery.  They  seem 
generally  crowded  together  toward  the  centre,  blend- 
ing into  a  continuous  blaze  of  light.  Yet,  although 
they  appear  so  densely  compacted,  it  is  probable 
that  if  we  could  change  our  stand-point,  penetrating 
one  of  these  groups  of  suns  we  should  find  it  open- 
ing up  and  spreading  out  before  us  on  our  approach, 
until,  in  the  midst,  the  suns  would  shine  down  upon 
us  from  the  heavens  as  the  stars  do  in  our  own  sky. 
NEBULAE. — These  are  faint  misty  objects  like  specks 
of  luminous  clouds.  They  are  generally  either  round 
or  oval,  and  brightest  at  the  centre.  They  differ 
from  "clusters"  in  not  being  resolvable  into  stars 
when  viewed  through  the  largest  telescopes.  With 
the  constant  improvement  made  in  these  instru- 
ments, however,  many  nebulae  have  been  resolved, 
and  thus  the  number  of  clusters  increased,  while  new 
nebulae  are  being  discovered  to  take  their  places. 
Until  of  late,  it  was  thought  that  all  nebulae  were 
simply  groups  of  stars,  which  would  be  ultimately 
discerned  in  the  more  powerful  telescopes  yet  to 
be  made.  Spectrum  analysis  shows,  however,  that 


NEBULJL 


273 


many  of  these  luminous  clouds  are  gaseous,  and  not 
solid.  They  cannot,  therefore,  be  suns.  Since  they 
maintain  the  same  position  with  respect  to  the  stars, 
their  distance  must  be  inconceivably  great,  and  in 
order  to  be  visible  to  us,  their  magnitude  must  be  pro- 
portionately vast.  They  are  most  abundant  at  the 
two  poles  of  the  Milky  Way,  but  are  more  uniformly 
distributed  over  the  heavens  lying  near  the  south 
pole.  Those  portions  of  the  sky  which  are  poorest 
in  stars,  are  richest  in  nebulae.  Herschel  was  ac- 
customed to  say  to  his  secretary,  whenever  for  a 
brief  time  he  saw  no  star  passing  the  field  of  his 
telescope,  as  in  the  diurnal  revolution  the  heavens 
swept  by  it,  "  Prepare  to  write ;  nebulae  are  about 
to  arrive." 

Nebulas  are  divided,  according  to  their  form,  into 
six  classes — elliptic,  annular,  spiral,  planetary,  irregu- 
lar nebulce,  and  nebulous  stars. 

The  elliptic,  or  merely  oval  nebulae,  are  the  most 
abundant.  Under  this  head  is  commonly  classe'd  the 
"  great  nebula  in  Andromeda,"  which  was  discov- 
ered over  a  thousand  years 
ago.  It  is  visible  to  the  naked 
eye.  Prof.  Bond,  of  the  Cam- 
bridge Observatory,  has  part- 
ly resolved  it  into  stars.  He 
has  distinctly  counted  1500, 
although  its  nebulous  appear- 
ance is  still  retained.  Under 
the  telescope  it  is  one  of  the 

12* 


NKBULA    IN    ANDROMEDA. 


274  THE  SIDEREAL  SYSTEM. 

most  glorious  objects  in  the  heavens.  "  If  we  sup- 
pose this  nebula  to  be  one  continuous  bed  of  stars 
of  different  sizes  for  its  entire  extent,  it  must 
comprise  the  enormous  number  of  30,000,000."  The 
distance  of  such  nebulae  from  the  earth  entirely  passes 
our  comprehension.  Some  astronomers  have  estima- 
ted that  a  ray  of  light  would  require  800,000  years  to 
span  the  gulf  that  intervenes.  Imagination  wearies* 
itself  in  the  attempt  to  understand  these  figures. 
They  only  teach  us  something  of  the  limitless  ex- 
panses of  that  space  in  which  God  is  working  the 
mysterious  problem  of  creation. 

The    annular    nebulce   have   the   form   of   a   ring. 
There  are  but  four  of  these  "ring  universes."     In 

Pig.  84. 


NEBULA    IN    LYRA. 


the  cut  is  a  representation  of  one  in  Lyra — first  as 
seen  by  Herschel,  and  having  in  the  centre  a  nebu- 
lous film  like  a  "bit  of  gauze  stretched  over  a  hoop ; " 
second,  as  .shown  in  Lord  Kosse's  great  telescope, 
which  resolves  the  filmy  parts  of  the  nebula  into  ex- 
cessively minute  stars,  and  reveals  a  fringe  of  stars 


CLUSTER  IN  CANBS   VEXATICT. 


276  THE  SIDEREAL  SYSTEM. 

along  the  edge.  Though  apparently  so  small,  its 
dimensions  must  be  enormous.  If  no  further  from 
the  earth  than  61  Cygni,  the  diameter  would  be 
2,000,000,000  miles.  It  is  probably  immensely  further 
distant. 

The  spiral  or  "  whirlpool  nebulae  "  are  exceedingly 
curious  in  their  appearance.  The  most  remarkable 
one  is  that  in  Canes  Venatici.  It  consists  of  brilliant 
spirals  sweeping  outward  from  a  central  nucleus, 
and  all  overspread  with  a  multitude  of  stars.  One 
is  lost  in  attempting  to  imagine  the  distance  of  such 
a  mass,  and  the  forces  which  produce  such  a  "  tre- 
mendous hurricane  of  matter — perhaps  of  suns." 

Planetary  nebulae,  by  their  circular  form  and  pale 
uniform  light,  resemble  the  disks  of  the  most  dis- 
tant planets  of  our  system.  Their  edges  are  gener- 
ally Avell  defined,  though  some- 
times  slightly  furred.  Three- 
fourths  of  them  are  in  the 
southern  hemisphere.  Several 
have  a  blue  tinge.  There  is 
one  in  Ursa  Major,  which  if  lo- 
cated at  the  distance  named 
before — that  of  61  Cygni — 
would  fill  a  space  equal  to 

.  PLANETARY  NEBULA. 

three  times  the  entire  orbit  of 

Neptune.  About  twenty-five  of  these  "island  uni- 
verses" •  have  been  found  scattered  through  the 
ocean  of  space.  Columbus  discovered  a  new  conti- 
nent, and  so  immortalized  his  name ;  what  shall  we 


NEBULA.  277 

say  of  the  astronomer  who  discovers  a  universe  of 
worlds  ? 

Irregular  nebulae  are  those  which  have  no  definite 
form.  Many  of  them  present  all  the  irregularities 
of  clouds  torn  and  FIg  87 

rent  by  the  tem- 
pest. Some  of  the 
likenesses  which 
may  be  traced  by 
the  fancy  are 
strangely  fantas- 
tic :  for  example, 
the  "  dumb-bell 
nebula"  in  the 
constellation  Vul- 
pecula,  and  the 
"crab  nebula" 
near  the  southern 

horn      of     TaurUS.  DUMB-BELL  NEBULA. 

There  is  also  one  known  as  "  the  great  nebula  in  the 
sword-handle  of  Orion,"^  in  which  may  be  seen  a 
faint  resemblance  to  the  wings  of  a  bird. 

Nebulous  stars  are  so  called  because  they  are  en- 
veloped by  a  faint  nebula,  usually  of  a  circular 
form.  The  star  is  generally  seen  at  the  centre,  al- 
though some  which  are  elliptical  surround  two  stars, 
one  in  each  focus.  It  is  thought  that  these  may 
be  suns  possessing  immense  atmospheres,  which  are 
rendered  visible  somewhat  as  that  of  our  sun  is  in 
the  zodiacal  light ;  and  that  in  like  manner  our  sun 


278 


THE   SIDEREAL   SYSTEM. 
Fig.  88. 


CRAB   NEBULA. 


itself  to  those  in  space  presents  the  appearance  of 
a  nebulous  star.  The  luminous  atmosphere  of  the 
star  in  Cygnus,  if  located  at  the  distance  of  a  Cen- 
tauri,  is  of  an  extent  equal  to  "  fifteen  times  the 
distance  of  Neptune  from  the  sun." 

Variable  nebulw. — Certain  changes  take  place  among 
the  nebulfc  which  can  be  accounted  for  only  under 


NEBUL2E.  279 

the  supposition  that  they,  like  some  of  the  stars,  are 
variable.  Mr.  Hind  tells  us  of  one  in  Taurus  which 
was  distinctly  visible  with  a  good  telescope  in  1852, 
but  in  1862  it  had  vanished  entirely  out  of  the  reach 
of  a  much  more  powerful  instrument.  It  seems  to 
have  disappeared  altogether.  The  great  nebula  in 
Argo,  when  observed  by  Herschel  in  1838,  had  in 
the  centre  a  vacant  space  containing  a  star  of  the 
first  magnitude  completely  enshrouded  by  nebulous 
matter.  In  1863,  the  nebulous  matter  had  disap- 
peared, and  the  star  was  only  of  the  sixth  magni- 
tude. These  facts  as  yet  defy  explanation.  They 
only  illustrate  the  vast  and  wonderful  changes  con- 
stantly taking  place  in  the  heavens. 

Double  ncbulce. — There  seems  to  be  a  physical  con- 
nection existing  between  some  of  the  nebulae,  similar 
to  that  already  noticed  in  respect  to  certain  stars. 
In  the  case  of  the  latter,  this  inter-relation  has  been 
proved,  since  their  movements  even  at  their  distances 
can  yet  be  traced  in  the  lapse  of  years.  "  But  owing 
to  the  almost  infinite  depths  in  the  abyss  of  the 
heavens  at  which  these  nebula)  exist,  thousands  of 
years,  perhaps  thousands  of  centuries,  would  be 
necessary  to  reveal  any  movement."  (Guillemin.) 

MAGELLANIC  CLOUDS. — Not  far  from  the  southern 
pole  of  the  heavens  there  are  two  cloud-like  masses, 
distinctly  visible  to  the  naked  eye,  known  to  naviga- 
tors as  "  Cape  Clouds."  Sir  John  Herschel  describes 
them  as  consisting  of  swarms  of  stars,  clusters,  and 
nebulae,  seemingly  grouped  together  in  the  wildest 


280  THE  SIDEREAL  SYSTEM. 

confusion.  In  the  larger,  he  found  582  single  stars, 
46  clusters,  and  291  nebulae. 

THE  MILKY  WAY  — Via  Lactea  or  Galaxy,  as  it  is 
variously  termed — is  that  luminous,  cloud-like  band 
that  stretches  across  the  heavens  in  a  great  circle. 
It  is  inclined  to  the  celestial  equator  about  63°,  and 
intersects  it  in  the  constellations  Cetus  and  Virgo. 
This  stream  of  suns  is  divided  into  two  branches 
from  a  Centauri  to  Cygnus.  To  the  naked  eye  it 
presents  merely  a  diffused  light ;  but  with  a  power- 
ful telescope  it  is  found  to  consist  of  myriads  of  stars 
densely  crowded  together.  These  stars  are  not  uni- 
formly distributed  through  its  entire  extent.  In 
some  regions,  within  the  space  of  a  single  square 
degree  we  can  discern  as  many  as  can  be  seen  with 
the  naked  eye  in  the  entire  heavens.  In  other  parts 
there  are  broad  open  spaces.  A  remarkable  instance 
of  this  occurs  near  the  Southern  Cross.  There  is  a 
dark  pear-shaped  vacancy  with  a  single  bright  star 
at  the  centre,  glittering  on  the  blue  background  of 
the  sky.  In  viewing  it,  one  is  said  to  be  impressed 
with  the  idea  that  he  is  looking  through  an  opening 
into  the  starless  depths  beyond  the  Milky  "Way. 

The  number  of  stars  in  the  galaxy  which  may  be 
seen  by  Herschel's  great  reflector  is  estimated  at 
twenty-one  and  a  half  .millions.  With  the  more 
powerful  instruments  now  being  made  it  is  probable 
the  number  will  be  largely  increased.  The  northern 
galactic  pole  is  situated  near  Coma  Berenices,  and 
the  southern  in  Cetus.  Advancing  from  either  pole 


THE   MILKY   WAY.  281 

toward  the  Milky  Way,  the  number  of  stars  increases, 
at  first  slowly  and  then  more  rapidly,  until  the  pro- 
portion at  the  galaxy  itself  is  thirty-fold. 

HerscheVs  theory. — Sir  W.  Herschel  has  conjec- 
tured that  the  stars  are  not  indifferently  scattered 
through  space,  but  are  collected  in  a  stratum  some- 
thing like  that  shown  in  the  cut,  and  that  our  sun 

Fig.  89. 


HERSCHEL'B  THEORY  OF  THE  MILKY  WAY. 

occupies  a  place  at  S,  near  where  the  stream  branches. 
A  and  E  are  the  galactic  poles.  It  is  evident  that, 
to  an  eye  viewing  the  stratum  of  stars  in  the  direc- 
tion SB,  SO,  or  SD,  they  would  seem  much  denser 
than  in  the  direction  SA  or  SE.  Thus  are  we  to 
think  of  our  own  sun  as  a  star  of  the  second  or  third 
magnitude,  and  our  little  solar  system  as  plunged 
far  into  the  midst  of  this  vortex  of  worlds,  a  mere 
atom  along  that 

"  Broad  and  ample  road 
Whose  dust  is  gold  and  parement  stare." 


282  THE  SIDEREAL  SYSTEM. 

NEBULAR  HYPOTHESIS. — This  is  a  theory  which  was 
advanced  by  Laplace,  to  show  how  the  solar  system 
was  formed.  In  the  "beginning,"  all  the  matter 
which  now  composes  the  sun  and  the  various  planets, 
with  their  moons,  was  in  a  gaseous  and  highly  heated 
state.  It  filled  all  the  space  now  occupied  by  the 
system,  and  extended  far  beyond  the  orbit  of  Nep- 
tune. In  other  words,  the  solar  system  was  simply 
an  immense  nebula.  The  heat,  which  is  the  repel- 
lant  force,  overcame  the  attraction  of  gravitation 
Gradually  the  mass  cooled  by  radiation.  As  centu- 
ries passed,  the  repellent  force  becoming  weaker,  the 
attractive  force  drew  the  matter  and  condensed  it 
toward  one  or  more  centres.  The  nebula  then 
presented  the  appearance  of  a  nebulous  star — a 
nucleus  enveloped  to  a  great  distance  by  a  gaseous 
atmosphere.  According  to  a  well-known  law  in 
philosophy,  seen  in  every-day  life,  in  a  whirlpool, 
a  whirlwind,  or  even  in  water  poured  into  a  funnel, 
wherever  matter  seeks  a  centre,  a  rotary  motion  is 
established.  As  this  rotary  motion  increased,  the 
centrifugal  force  finally  overcame  at  the  exterior  the 
attraction  of  gravitation,  and  so  threw  off  a  ring  of 
condensed  vapor.  Centuries  elapsed,  and  again,  un- 
der the  same  conditions,  a  second  ring  was  detached. 
Thus,  one  by  one,  concentric  rings  were  separated 
from  the  parent  nebula,  all  revolving  in  the  same 
plane  and  in  the  same  direction.  These  different 
rings,  becoming  gradually  consolidated,  formed  the 
planets, — generally  however,  in  this  process,  while 


NEBULAR  HYPOTHESIS.  283 

still  in  the  vaporous  state  and  slowly  condensing, 
themselves  throwing  off  rings  which  were  in  turn 
consolidated  into  satellites.  In  the  case  of  Saturn, 
several  of  these  secondary  rings  did  not  break  up, 
and  so  condense  into  globes,  but  still  remain  as 
rings  which  revolve  about  the  planet.*  Mitchell 
naively  remarks,  "Saturn's  rings  were  left  un- 
finished to  show  us  how  the  world  was  made." 
The  ring  which  formed  the  minor  planets  broke  up 
into  small  fragments,  none  large  enough  to  attract 
the  rest  and  thus  form  a  single  globe.  The  central 
mass  of  vapor  finally  condensed  itself  into  the  sun, 
which  remains  the  largest  member  of  the  system. 
According  to  this  theory,  the  sun  may  yet  give  off 
a  few  more  planets,  whose  orbits  will  not  exceed  its 
present  diameter.  After  a  time  its  heat  will  have  all 
been  radiated  into  space,  its  fire  will  become  extinct, 
and  life  on  the  planets  will  cease.  We  know  not 
when  this  remote  event  may  occur.  We  cannot 
fathom  the  purpose  of  God  in  creating  and  main- 
taining this  system  of  worlds,  nor  foretell  how  soon  it 
may  complete  its  mission.  We  are  assured,  however, 

"  That  nothing  walks  with  aimless  feet, 
That  not  one  life  shall  be  destroyed, 
Or  cast  as  rubbish  to  the  void, 
When  God  hath  made  the  pile  complete." 

In  Memoriam. 

*  It  is  possible  that  these  rings  may  yet  break  up  and  form 
new  satellites  for  that  planet.  Indeed,  some  hold  that  one  at 
least  of  the  rings  has  thus  been  resolved  into  small  meteorites. 
These  may  be  attracted,  and  so  picked  up,  one  by  one,  by  the  larger 
in  succession,  until  they  form  another  moon,  which  will  continue 
to  revolve  about  the  planet  as  the  ring  does  now. 


284 


THE   SIDEREAL  SYSTEM. 

Fig.  90. 


CELESTIAL    CHEMISTEY. 

SPECTRUM  ANALYSIS. — The  rainbow — that  child  of 
the  sun  and  shower — is  familiar  to  all.  The  brilliant 
band  of  colors,  seen  when  the  sunbeam  is  passed 
through  a  prism,  is  scarcely  less  beautiful.  The  ray 
of  light  containing  the  primary  colors  is  spread  out 
fan-like,  and  each  tint  reveals  itself.  This  variously 
colored  band  is  called  in  philosophy  a  spectrum  (plu- 
ral, spectra).  There  are  three  different  kinds  of 
spectra — 

1st.   When  the  light  of  a  solid  or  liquid  body,  as 


CELESTIAL   CHEMISTRY.  285 

iron  white-hot,  is  passed  through  a  prism,  the  spec- 
trum is  continuous,  and  consists  of  a  series  of  distinct 
colors,  varying  from  red  on  one  side  to  violet  on  the 
other. 

2d.  If  the  light  of  a  burning  gas  containing  any 
volatilized  substance  be  passed  through  a  prism,  the 
spectrum  is  not  continuous,  but  is  ornamented  by 
bright-colored  lines—  sodium  giving  two  yellow 
lines,  strontia  a  red  one,  silver  two  beautiful  green 
ones.  Each  element  produces  a  definite  series 
which  can  be  readily  recognized  as  its  test. 

3d.  If  a  light  of  the  first  kind  be  passed  through 
one  of  the  second,  the  spectrum  will  be  found  to  be 
crossed  by  dark  lines.  Thus,  if  the  white  light  of  a 
burning  match  be  passed  through  a  flame  containing 
sodium,  instead  of  the  vivid  yellow  lines  so  charac- 
teristic of  that  metal,  two  black  lines  will  exactly 
occupy  their  place.  A  gaseous  flame  absorbs  the  rays 
of  the  same  color  that  it  emits. 

THE  SPECTROSCOPE. — This  instrument  consists  of 
two  small  telescopes,  with  a  prism  mounted  between 
their  object-glasses,  in  the  manner  shown  in  the  cut. 
The  rays  of  light  enter  through  a  narrow  slit  at  A 
and  are  rendered  parallel  by  the  object-glass.  They 
then  pass  through  the  prisms  at  C,  are  separated  into 
the  different  colors,  and  entering  the  second  telescope 
at  D,  fall  upon  the  eye  at  B.  A  third  telescope  is 
sometimes  attached,  which  contains  a  minutely  accu- 
rate scale  for  measuring  the  distances  of  the  lines.  In 
addition,  a  mirror  may  throw  in  a  ray  of  sunlight  or 


286  THE  SIDEREAL  SYSTEM. 

starlight  at  one  side  of  the  slit,  and  so  we  can  com- 
pare the  spectrum  of  the  sunbeam  with  that  of  any 
flame  we  desire. 

Vis.  91 


A  SPECTROSCOPE. 


Revelations  of  the  spectroscope  concerning  the  sun. — 
The  spectrum  of  the  sunbeam  is  not  continuous,  but 
is  crossed  by  a  large  number  of  dark  lines,  called, 
from  their  discoverer,  Fraunhofer's  lines.  It  is  there- 
fore concluded  that  the  sun's  light  is  of  the  third 
class  just  named,  and  that  it  is  produced  by  the  vivid 
light  of  a  highly  heated  body  shining  through  a 
flame  full  of  volatilized  substances.  But  not  only 
does  spectrum  analysis  thus  shed  light  on  the  phys- 
ical constitution  of  the  sun,  but  these  lines  are  so 
distinctive,  so  marked  and  varied,  that  the  very  ele- 
ments of  which  the  sun  is  composed  may  be  dis- 
covered. Thus,  for  example,  iron  gives  a  spectrum 
of  some  70  lines,  differing  in  intensity  and  relative 
length.  These  are  bright  when  iron  vapor  is  burn- 


CELESTIAL   CHEMISTRY.  287 

ing,  and  dark  when  white  light  is  passed  through 
such  burning  vapor.  In  the  solar  spectrum  we  have 
the  perfect  coincidence  of  70  dark  lines,  line  for  line 
and  strength  for  strength.  The  conclusion  is  irre- 
sistible that  iron  is  contained  in  the  sun's  atmos- 
phere. The  following  include  all  the  elements  that 
are  now  known  to  exist  in  it : 

Sodium,  Iron,  Strontium 

Calcium,  Chromium,  Cadmium, 

Barium,  Nickel,  Cobalt, 

Magnesium,  Zinc,  Hydrogen. 

STARS  ARE  SUNS. — The  same  method  of  analysis 
has  been  apph'ed  to  the  stars.  Their  spectra  also 
are  marked  by  dark  lines.  Their  constitution  is 
therefore  like  our  sun ;  they  contain  also  the  same 
familiar  elements.  Aldebaran  seems  the  most  like 
our  earth.  It  has  at  least  nine  elements  known  to 
chemists  : 

Sodium,  Iron,  Magnesium, 

Hydrogen,  Bismuth,  Antimony, 

Tellurium,  Mercury,  Calcium. 

Betelgeuse  contains  many  elements  known  to  us, 
but  no  hydrogen. — What  a  world  that  must  be  with- 
out water !  Arcturus,  Kutherford  says,  closely  re- 
sembles our  sun. 

We  thus  trace  in  the  faintest  star  that  trembles  in 
the  measureless  depths  of  space  the  same  elements 
that  compose  the  food  we  eat  and  the  water  \ve 
drink.  We  know  that  we  are  akin  to  nature  every- 
where— that  we  are  a  part  of  a  system  vast  as  the 
universe. 


288  THE   SIDEREAL  SYSTEM. 

SPECTRA  OF  NEBUKE. — Instead  of  being  marked 
with  dark  lines,  as  are  the  spectra  of  the  stars,  many 
of  these  exhibit  bright  lines.  Their  spectra  are  of  the 
2d  kind.  This  proves  the  nebula  to  consist,  not,  like 
the  stars,  of  an  intensely  heated  solid  body  shining 
through  aluminous  atmosphere,  but  of  a  glowing  mass 
of  gas.  Out  of  60  nebulae  examined  by  Mr.  Huggins, 
20  exhibited  the  bright  lines  belonging  to  the  gases, 
and  all  contained  nitrogen. 

It  is  possible  in  this  manner  even  to  decide  the 
relative  brightness  of  the  different  nebulae.  The 
dumb-bell  nebula  was  found  to  emit  a  light  only 
about  one  twenty-thousandth  part  that  of  a  common 
wax-candle.  If  this  matter  be  a  "sun-germ,"  how 
immensely  must  it  become  condensed  before  its 
rushlight  glimmering  can  rival  the  dazzling  brilliancy 
of  even  our  own  sun! 

THE  SOLAR  FLAMES,  which  before  were  seen  only 
at  an  eclipse,  can  now  be  examined  at  any  time. 
The  sun  is  a  sea  of  fire.  Flames  travel  over  its  sur- 
face faster  than  the  earth  in  its  orbit :  one  shot  out 
80,000  miles  and  disappeared  in  ten  minutes.  Such 
tremendous  convulsions  surpass  all  terrestrial  phe- 
nomena. 

TIME. 

SIDEREAL  TIME. — A  sidereal  day  is  the  exact  in- 
terval of  time  in  which  the  earth  revolves  on  its  axis. 
It  is  found  by  marking  two  successive  passages  of  a 
star  across  the  meridian  of  any  place.  This  is  so 


TIME.  289 

• 

absolutely  uniform,  that  the  length  of  the  sidereal 
day  has  not  varied  T|^  of  a  second  in  2,000  years. 
The  sidereal  day  is  divided  into  twenty-four  equal 
portions,  which  are  called  sidereal  hours,  and  each 
of  these  into  sixty  portions,  termed  sidereal  min- 
utes, etc. 

Astronomical  docks  are  regulated  to  keep  sidereal 
time.  The  day  commences  when  the  vernal  equinox 
is  on  the  meridian.  Therefore,  the  time  by  the  si- 
dereal clock  does  not  in  any  way  point  out  the  hour 
of  the  ordinary  day.  It  only  indicates  how  long  it 
is  since  the  vernal  equinox  crossed  the  meridian,  and 
thus  always  shows  the  right  ascension  of  any  star 
which  may  happen  to  be  on  the  meridian  at  that 
moment.  The  hours  of  the  clock  are  easily  reduced 
to  degrees  (see  p.  38).  The  astronomer  always 
reckons  the  hours  of  the  day  consecutively  up  to 
twenty-four. 

SOLAR  TIME. — A  solar  day  is  the  interval  between 
two  successive  passages  of  the  sun  across  the  me- 
ridian of  any  place.  If  the  earth  were  stationary  in 
its  orbit,  the  solar  day  would  be  of  the  same  length 
as  the  sidereal  >  but  while  the  earth  is  turning  around 
on  its  axis,  it  is  going  forward  at  the  rate  o-:  360°  in 
a  year,  or  about  1°  per  day.  When  the  earth  has 
made  a  complete  revolution,  it  must  therefore  per- 
form a  part  of  another  revolution  through  this  ad- 
ditional degree,  in  order  to  bring  the  same  meridian 
vertically  under  the  sun.  One  degree  of  diurnal 
revolution  is  about  equal  to  four  minutes  of  time, 

13 


290  THE  SIDEREAL  SYSTEM. 

H 

Hence  the  solar  day  is  about  four  minutes  longer 
than  the  sidereal  day.  For  the  convenience  of  so- 
ciety, it  is  customary  to  call  the  solar  day  24  hours 
long,  and  make  the  sidereal  day  only  23  hr.  56  min. 
4  sec,  in  length,  expressed  in  mean  solar  time.  A 
sidereal  day  being  shorter  than  a  solar  one,  the  si- 
dereal hours,  minutes,  etc.,  are  shorter  than  the 
solar ;  24  hours  of  mean  solar  time  being  equal  to 
24  hr.  3  min.  56  sec.  of  sidereal  time. 

From  what  has  been  said,  it  follows  that  the  earth 
makes  366  revolutions  around  its  axis  in  365  solar 
days. 

MEAN  SOLAR  TIME. — The  solar  days  are  of  unequal 
length.  To  obviate  this  difficulty,  astronomers  sup- 
pose a  mean  sun  moving  through  the  equator  of  the 
heavens  (which  is  a  circle  and  not  an  ellipse)  with  a 
perfectly  uniform  motion.  When  this  mean  sun 
passes  the  meridian  of  any  place,  it  is  mean  noon ; 
and  when  the  true  sun  is  in  the  same  position,  it  is 
apparent  noon.  This  day  is  the  average  length  of  all 
the  solar  days  in  the  year.  The  clocks  in  common 
use  are  regulated  to  keep  mean  time.  When,  there- 
fore, it  is  twelve  by  the  clock,  the  sun  may  be  either 
a  little  i  ast  or  a  little  behind  the  meridian.  The 
difference  between  the  sun-time  (apparent  solar- 
time)  and  the  clock-time  (mean  time),  is  called  the 
" equation  of  lime"  This  is  the  greatest  about  the 
first  of  November,  when  the  sun  is  sixteen  and  a 
quarter  minutes  in  advance  of  the  clock.  The  sun 
is  the  slowest  about  February  10th,  when  it  is  about 


TIME.  291 

fourteen  and  a  half  minutes  behind  mean  time. 
Mean  and  apparent  time  coincide  four  times  in  the 
year — namely,  April  15th,  June  15th,  September  1st, 
and  December  24th.  On  those  days  the  noon-mark 
on  the  sun-dial  coincides  with  twelve  o'clock.  In 
France,  until  1816,  apparent  time  was  used ;  and  the 
confusion  was  so  great,  that  Arago  relates  how  the 
town  clocks  would  differ  thirty  minutes  in  striking  the 
same  hour.  As  the  time  varied  every  day,  no  watch- 
maker could  regulate  a  watch  or  clock  to  keep  it. 

THE  SUN-DIAL — The  apparent  time  of  the  dial  may 
be  readily  changed  to  mean  time,  by  adding  or  sub- 
tracting the  number  of  minutes  given  in  the  almanac 
for  each  day  in  the  year,  under  the  heading  "  sun 
slow"  or  "sun  fast."  As  a  noon-mark  is  thus  a 
very  convenient  method  of  regulating  a  timepiece, 
especially  in  the  country,  the  following  manner  of  ob- 
taining one  without  a  transit  instrument  may  be 
useful. 

Select  a  level  hard  surface  which  is  exposed  to  the 
sun  from  about  9  A.  M.  to  3  p.  M.  Upon  this  carefully 
describe,  with  compasses,  a  circle  of  eight  or  ten 
inches  in  diameter.  Take  a  piece  of  heavy  wire,  six 
or  eight  inches  in  length,  one  end  of  which  is 
sharpened.  Drive  this  perpendicularly  into  the  cen- 
tre of  the  circle,  leaving  it  just  high  enough  to  allow 
the  extreme  end  of  its  shadow  to  fall  upon  the  circle 
about  9  J  or  10  A.  M.  Mark  this  point,  and  also  the  place 
where  the  shadow  touches  the  circle  in  the  afternoon. 
Take  a  point  half-way  between  the  two,  and  drawing 

- 


292 


THE  SIDEREAL  SYSTEM. 


a  line  from  that  to  the  centre  of  the  circle,  it  will 
be  the  meridian  line  or  noon-mark. 

WHY   THE  SOLAR  DAYS  ARE  OF  UNEQUAL  LENGTH. — 

There  are  two  reasons  for  this — the  unequal  orbital 
motion  of  the  earth  and  the  obliquity  of  the  ecliptic. 
First :  the  orbit  of  the  earth  is  an  ellipse  ;  and  thus 
I  lie  apparent  yearly  motion  of  the  sun  along  the 
ecliptic  is  variable.  In  perihelion,  in  January,  the 
sun  appears  to  move  eastward  daily  1°  1'  9.9"  ;  while 
at  aphelion,  in  July,  only  57'  11.5".  As  the  earth 
in  its  diurnal  motion  revolves  uniformly  from  west  to 
east,  and  the  sun  passes  eastward  irregularly,  this 
must  produce  a  corresponding  variation  in  the 
length  of  the  solar  day.  The  sun,  therefore,  comes 
to  the  meridian  sometimes  earlier  and  sometimes 
later  than  the  mean  noon,  and  they  agree  only  at 
perihelion  and  aphelion. 

Second :  as  we  have  just  seen,  the  mean  sun  is  sup- 
posed to  move  in  a  circle  and  not  an  ellipse.  This 
would  make 
the  motion 
along  the 
ecliptic  uni- 
form, but  the 
obliquity  of 
the  ecliptic 
would  still 
cause  an  ir- 


N       M     L     K 


regularity  in  the  length  of  the  day.     The  mean  sun 
is  therefore  supposed  to  pass  along  the  equinoctial, 


TIME.  293 

which  is  perpendicular  to  the  earth's  axis ;  while  the 
ecliptic  is  inclined  to  it  23°  28'.  Let  A  represent  the 
vernal  equinox,  I  the  autumnal,  AEI  the  ecliptic, 
AI  the  equinoctial,  PK,  PL,  PM,  etc.,  meridians. 
Let  the  distances  AB,  BC,  CD,  etc.,  be  equal  arcs  of 
the  ecliptic,  which  are  passed  over  by  the  sun  in 
equal  times.  Next,  mark  off  on  the  equinoctial  dis- 
tances Aa,  dbt  &c,  etc.,  equal  to  AB,  BO,  etc.  These 
are  equal  arcs  of  right  ascension,  or  hour-circles, 
through  which  the  earth,  revolving  from  west  to  east, 
passes  in  equal  times.  Now,  meridians  drawn  through 
these  divisions,  would  not  agree  with  those  drawn 
through  equal  divisions  on  the  ecliptic.  Hence,  a  sun 
moving  along  the  ecliptic,  which  is  inclined,  would  not 
make  equal  days,  even  though  the  ecliptic  were  a  per- 
fect circle.  Let  us  see  how  the  mean  and  apparent 
solar  days  would  compare.  Let  the  real  sun  pass  in 
its  eastward  course  from  A  to  B  in  a  certain  time,  the 
mean  sun  moving  the  same  distance  would  reach  the 
point  a,  since  the  latter  travels  on  the  base  and  tho 
former  the  hypothenuse  of  a  triangle.  The  earth,  re- 
volving from  west  to  east,  would  cause  the  real  sun 
to  cross  any  meridian  earlier  than  the  mean  sun ; 
hence,  apparent  time  would  be  faster  than  clock-time. 
By  holding  the  figure  up  above  us  toward  the 
heavens,  we  can  see  how  a  westerly  sun  would  cross 
the  meridian  earlier  than  an  easterly  one.  Follow- 
ing the  same  reasoning,  we  can  see  that  at  the  sol- 
stice, solar  and  mean  time  would  agree;  while 
beyond  that  point  the  mean  time  would  be  faster. 


294  THE  SIDEREAL  SYSTEM. 

THE  CIVIL  DAY.— This  is  the  .mean  solar  day  of 
which  we  have  spoken.  It  extends  from  midnight 
to  midnight.  The  present  method  of  dividing  the 
day  into  two  portions  of  twelve  hours  each,  was 
adopted  by  Hipparchus,  150  years  B.  c.,  and  is  now 
in  general  use  over  the  civilized  world.  Until  re- 
cently, however,  very  many  nations  terminated  one 
day  and  commenced  the  next  at  sunset.  Under  this 
plan,  10  o'clock  on  one  day  would  not  mean  the  same 
as  10  o'clock  on  another  day.  The  Puritans  com- 
menced the  day  at  6  P.  M.  The  Babylonians,  Per- 
sians, and  modern  Greeks  begin  the  day  at  sunrise. 
The  names  of  the  days  now  in  use  are  derived  as 
follows : 

1.  Dies  Solis ( Latin ) . . . .  Sun's  day. 

2.  Dies  Lunae (     "    ).... Moon's  day. 

8.  Tius  daeg (Saxon) Tius's  day. 

4.  Wodnes  daeg. . .(    "    ) . . . .  Woden's  day. 
6.  Thames  daeg . .  (     "     ) Thor's  day. 

6.  Friges  daeg (    "    ) Friga's  day. 

7.  Dies  Saturni . . .  ( Latin ) . . . .  Saturn's  day. 

THE  TEAR. — The  sidereal  year  is  the  interval  of  a 
complete  revolution  of  the  earth  about  the  sun,  meas- 
ured by  a  fixed  star.  It  comprises  365  d.,  6hrs., 
9  min.,  9.6  sec.  of  mean  solar  time.  The  mean  solar 
year  (tropical  year)  is  the  interval  between  two  suc- 
cessive passages  of  the  sun  through  the  vernal  equi- 
nox. It  comprises  365  d.,  5hrs.,  48  min.,  49.7  sec. 
If  the  equinoxes  were  stationary,  there  would  be  no 
difference  between  the  sidereal  and  tropical  year. 
As  the  equinoxes  retrograde  along  the  ecliptic  50"  of 
space  annually,  the  former  is  20  min.,  20  sec.  longer. 


TIME.  295 

The  anomalistic  year  is  the  interval  between  two 
successive  passages  of  the  earth  through  its  perihe- 
lion. It  is  4  min.,  40  sec.  longer  than  the  sidereal 
year. 

THE  ANCIENT  YEAR. — The  ancients  ascertained 
the  length  of  the  year  by  means  of  the  gnomon.  This 
was  a  perpendicular  rod  standing  on  a  smooth  plane 
on  which  was  a  meridian  line.  "When  the  shadow 
cast  on  this  line  was  the  shortest,  it  indicated  the 
summer  solstice ;  and  when  it  was  the  longest,  the 
winter  solstice.  The  number  of  days  required  for 
the  sun  to  pass  from  one  solstice  back  to  it  again  de- 
termined the  length  of  the  year.  This  they  found 
to  be  365  days.  As  that  is  nearly  six  hours  less  than 
the  true  solar  year,  dates  were  soon  thrown  into  con- 
fusion. If,  at  a  certain  date  the  summer  solstice  oc- 
curred on  the  20th  June,  in  four  years  it  would  fall 
on  the  21st ;  and  thus  it  would  gain  one  day  every 
four  years,  until  in  time  the  summer  solstice  would 
happen  in  the  winter  months. 

JULIAN  CALENDAR. — Julius  Caesar  first  attempted 
to  make  the  calendar  year  coincide  with  the  motions 
of  the  sun.  By  the  aid  of  Sosigenes,  an  Egyptian 
istronomer,  he  devised  a  plan  of  introducing  every 
fourth  year  a  leap-year,  which  should  contain  an 
sxtra  day.  This  was  termed  a  bissextile  year,  since 
'iie  sixth  (sextilis)  day  before  the  kalends  (first  day) 
Of  March  was  then  counted  twice. 

GREGORIAN  CALENDAR. — Though  the  Julian  calen- 
dar was  nearly  perfect,  it  was  yet  somewhat  defec- 


296  THE  SIDEREAL  SYSTEM. 

tive.  It  considered  the  year  to  consist  of  365J  days, 
which  is  11  min.  in  excess.  This  accumulated  year 
by  year,  until  in  1582  the  difference  amounted  to 
ten  days.  In  that  year,  the  vernal  equinox  occurred 
on  the  llth  of  March,  instead  of  the  21st.  Pope 
Gregory  undertook  to  reform  the  anomaly,  by  drop- 
ping ten  days  from  the  calendar  and  ordering  that 
thereafter  only  centennial  years  which  are  divisible 
by  400  should  be  leap-years.  The  Gregorian  calen- 
dar was  generally  adopted  in  all  Catholic  countries. 
Protestant  England  did  not  accept  the  change  until 
1752.  The  difference  had  then  amounted  to  11  days. 
These  were  suppressed  and  the  3d  of  September 
was  styled  the  14th. 

Dates  reckoned  according  to  the  Julian  calendar 
are  termed  Old  Style  (O.  S.),  and  those  according  to 
the  Gregorian  calendar  New  Style  (N.  S.)  This 
sweeping  change  was  received  in  England  with  great 
dissatisfaction.  Prof.  De  Morgan  narrates  the  fol- 
lowing. "A  worthy  couple  in  a  country  town,  scandal- 
ized by  the  change  of  the  calendar,  continued  for 
many  years  to  attempt  the  observance  of  Good  Fri- 
day on  the  old  day.  To  this  end  they  walked  seri- 
ously and  in  full  dress  to  the  church  door,  on  which 
the  gentleman  rapped  with  his  stick.  On  finding  no 
admittance,  they  walked  as  seriously  back  again  and 
read  the  service  at  home.  There  was  a  wide-spread 
superstition  that,  when  Christmas  day  began,  the 
cattle  fell  on  their  knees  in  their  stables.  It  was  as- 
serted that,  refusing  to  change,  they  continued  their 


TIME.  297 

prostrations  according  to  the  Old  Style.  In  Eng- 
land, the  members  of  the  government  were  mobbed 
in  ihd  streets  by  the  crowd,  which  demanded 
the  eleven  days  of  which  they  had  been  illegally 
depiived." 

COMMENCEMENT  or  THE  TEAK. — The  Jews  began 
thoir  civil  year  with  the  autumnal  equinox,  but  their 
ecclesiastical  with  the  vernal.  When  Caesar  revised 
the  calendar,  among  the  Romans  the  year  com- 
menced with  the  winter  solstice  (Dec.  22),  and  it  is 
probable  he  did  not  intend  to  change  it  materially. 
He,  however,  ordered  it  to  date  from  January  1st,  in 
order  that  the  first  year  of  his  new  calendar  should 
begin  with  the  day  of  the  new  moon  immediately 
succeeding  the  winter  solstice. 

THE  EARTH  OUR  TIMEPIECE. — The  measure  of  time 
is,  as  we  have  just  seen,  the  length  of  the  mean 
day.  That  is  estimated  from  the  length  of  the  si- 
dereal day.  Hence  the  standard  for  time  is  the  rev- 
olution of  the  earth  on  its  axis.  All  weights  and 
measures  are  based  on  time.  An  ounce  is  the  weight 
of  a  given  bulk  of  distilled  water.  This  is  measured 
by  cubic  inches.  The  inch  is  a  definite  part  of  the 
length  of  a  pendulum  which  vibrates  seconds  in  the 
latitude  of  London.  Arago  remarks,  a  man  would 
be  considered  a  maniac  who  should  speak  of  the  in- 
fluence of  Jupiter's  moons  on  the  cotton  trade.  Yet 
there  is  a  connection  between  these  incongruous 
ideas.  The  navigator,  travelling  the  waste  of  waters 
where  there  are  no  paths  and  no  guide-boards,  may 

13* 


298  THE  SIDEREAL  SYSTEM. 

reckon  his  longitude  by  the  eclipses  of  Jupiter's 
moons,  and  so  decide  the  fate  of  his  voyage.  We 
can  easily  see  how  the  revolution  of  the  earth  on  its 
axis  influences  the  cost  of  a  cup  of  tea. 


CELESTIAL  MEASUEEMENTS. 

Many  persons  read  the  enormous  figures  which 
indicate  the  distances  and  dimensions  of  the  heaven- 
ly bodies  with  an  indefinite  idea,  which  conveys  no 
such  feeling  of  certainty  as  is  experienced  when 
they  read  of  the  distance  between  two  cities,  or  the 
number  of  square  miles  in  a  certain  State.  Many, 
*oo,  imagine  that  celestial  measurements  are  so  mys- 
terious in  themselves  that  no  common  mind  can 
hope  to  grasp  the  methods.  Let  us  attempt  the  so- 
lution of  a  few  of  these  problems. 

1st.   TO  FIND  THE  DISTANCES  OF  THE  PLANETS  FROM 

THE  SUN. — In  the  figure,  E  represents  the  earth,  ES 
the   earth's  distance  from  Pig.  93. 

the  sun,  V  the  planet  Ve- 
nus, and  YES  the  angle  of 
elongation  (a  right-angled 
triangle).  It  is  clear,  that 
as  Yenus  swings  apparent- 
ly east  and  west  of  the  sun, 
this  angle  may  be  easily 
measured ;  also,  that  it  will 
be  the  greatest  when  Yenus 

0  COMPARATIVE  DISTANCE  OF  VEKU9 

is  in  aphelion  and  the  earth  ANB  THE  EARTH- 


CELESTIAL  MEASUBEMENTS.  299 

in  perihelion  at  the  same  time,  for  then  VS  will  be 
the  longest  and  VE  the  shortest.  Now  in  every 
right-angled  triangle  the  proportion  between  the 
h  jpothenuse,  ES,  and  the  side  opposite,  VS,  changes 
as  the  angle  at  E  varies,  but  with  the  same  angle  re- 
mains the  same  whatever  may  be  the  length  of  the 
lines  themselves.  This  proportion  between  the  hy- 
pothenuse  and  the  side  opposite  any  angle  is  termed 
the  sine  of  that  angle.  Tables  are  published  which 
contain  the  sines  for  all  angles.  In  this  way,  the 
mean  distance  of  Yenus  is  found  to  be  •££$*  that  of 
the  earth,  Mars  f  times,  Jupiter  5£  times,  etc. 

The  same  result  would  be  obtained  by  the  use  of 
Kepler's  third  law;  and  on  page  29,  we  saw  how 
the  distances  of  the  planets  themselves  could  be  de- 
termined by  the  periodic  times,  if  the  distance  of 
the  earth  from  the  sun  is  first  known.  So  that 
when  we  have  accurately  determined  the  sun's  dis- 
tance from  us,  we  can  then  decide  by  either  of  the 
methods  named  the  distance  of  all  the  planets.  In- 
deed that  is,  as  already  remarked,  the  "  foot-rule" 
for  measuring  all  celestial  distances. 

2d.   TO    MEASURE    THE  MOON'S    DISTANCE  FROM   THE 

EARTH. — (1.)  The  ancient  method. — As  the  moon's  dis- 
tance is  so  much  less  than  that  of  the  other  heavenly 
bodies,  it  is  measured  by  the  earth's  semi-diameter. 


*  If  the  pupil  has  studied  Trigonometry,  he  may  apply  here 
the  simple  proportion — 

ES  :  VS  : :  Radius  :  Sine  of  47*  15"  =  greatest  elongation  of  Venus. 


300  THE  SIDEREAL  SYSTEM. 

The  method,  an  extremely  rough  one,  which  was  in 
use  among  the  ancients,  was  something  like  the  fol- 
lowing. In  an  eclipse  of  the  moon,  that  body  passes 
through  the  earth's  shadow  in  about  four  hours.  If, 
then,  the  moon  travels  along  its  orbit  in  four  hours 
a  distance  equal  to  the  diameter  of  the  earth,  in 
twenty-four  hours  it  would  pass  over  six  times,  and 
in  a  lunar  month  (about  thirty  days)  one  hundred 
and  eighty  times,  that  distance.  The  circumference 
of  the  lunar  orbit  must  be  then  one  hundred  and 
eighty  times  the  diameter  of  the  earth.  The  ancients 
supposed  the  heavenly  orbits  to  be  circles,  and  as 
the  diameter  of  a  circle  is  about  J  of  the  circum- 
ference, they  deduced  directly  the  diameter  of  the 
moon's  orbit  as  120  times,  and  the  distance  of  the 
the  moon  from  the  earth  as  60  times  the  semi-diam- 
eter of  the  earth. 

(2.)  Modern  method  by  ihe,  lunar  parallax. — Under 
the  head  of  parallax  we  saw  how,  in  common  life, 
we  obtain  a  correct  idea  of  the  distance  of  an  object 
by  means  of  our  two  eyes.  We  proved  that  one  eye 
alone  gives  no  notion  of  distance.  Just,  then,  as  we 
use  two  eyes  to  find  how  far  from  us  an  object  is,  so 
the  astronomer  uses  two  astronomical  eyes  or  obser- 
vatories, located  as  far  apart  as  possible,  to  find  the 
parallax  of  a  heavenly  body.  In  the  figure,  M  rep- 
resents the  moon/  G  an  observatory  at  Greenwich, 
and  C  another  at  the  Cape  of  Good  Hope.  At  the 
former,  the  distance  from  the  north  pole  to  the 
centre  of  the  moon,  measured  on  a  meridian  of  the 


CELESTIAL   MEASUREMENTS. 


301 


celestial  sphere,  is  found  to  be  108°.  At  the  latter 
station,  the  distance  from  the  south  pole  to  the 
moon's  centre  is  measured  in  the  same  way,  and 
found  to  be  73J°.  The  sum  of  these  angles  is  181^°. 
Now,  the  entire  distance  from  the  north  pole  around 
to  the  south  pole,  measured  on  a  meridian,  can  be 
only  half  a  great  circle,  or  180°.  This  difference  of 


Pig.  94. 


P'  Z' 

MEASURING  MOON'S  DISTANCE  FROM  THE  EARTH. 

1J°  must  be  the  difference  in  the  position  of  the 
moon,  as  seen  from  the  two  observatories.  For  the 
observer  at  the  former  station  will  see  the  moon 
projected  on  the  celestial  sphere  at  G',  and  in  meas- 
uring its  distance  from  the  north  pole  will  measure 
an  arc  bG'  further  than  if  he  were  located  at  E,  the 
centre  of'  the  earth.  The  observer  at  the  latter  sta- 
tion will  see  the  moon  projected  on  the  celestial 
sphere  at  C',  and  in  measuring  its  distance  from  the 


302  THE  SIDEREAL  SYSTEM. 

south  pole  will  measure  an  arc  bC'  more  than  if  he 
were  located  at  E,  the  centre  of  the  earth.  The  sum 
of  bG'  and  bC'=  G'C'  is  the  difference  in  the  position 
of  the  moon  as  seen  from  the  two  stations.  In  other 
words,  it  is  the  moon's  parallax.  The  arc  G'C' 
measures  the  angle  C'MG';  that  angle  is  equal  to 
the  opposite  angle  GMC  =  1J°.  Now,  in  the  four- 
sided  figure  GECM,  the  sides  GE  and  CE  are  each 
equal  radii  of  the  earth  =  3956  miles ;  while  the  dis- 
tance from  G  to  C  is  the  difference  in  the  latitude  of 
the  two  places.  The  angles  ZGM  and  Z'CM,  being 
the  zenith  distances  of  the  moon,  are  known,  and  so 
the  angles  MGE  and  MCE  are  easily  found.  EM, 
the  moon's  distance  from  the  centre  of  the  earth,  is 
thus  readily  computed  by  a  simple  trigonometrical 
formula. 

(3.)  The  horizontal  paraUax  of  the  moon  is  most  com- 
monly found  by  estimating  its  distance,  not  from  the 
north  and  south  poles,  as  just  explained  under  the 
general  meaning  of  the  term  parallax,  but  from  a 
fixed  star.  The  moon's  horizontal  parallax  is  now 
estimated  at  57',  which  makes  its  distance  about 
sixty  times  the  earth's  semi-diameter.* 

To    FIND    THE  SUN'S    DISTANCE  FROM  THE  EARTH. — 

This  might  be  estimated  by  obtaining  the  solar 

*  In  figure  95,  let  S  represent  the  moon,  sun,  or  any  other 
heavenly  body,  AB  the  semi-diameter  of  the  earth,  and  ASB  the 
"  horizontal  parallax"  of  the  body.  Then,  by  the  following  trig- 
on  ometrical  formula,  the  distance  from  the  earth  may  be  easily 

calculated — 

AS  :  AB  : :  Radius  :  Sin  of  ABB. 


CELESTIAL  MEASUREMENTS.  303 

parallax  in  the  same  manner  as  the  lunar  parallax. 
It  would  be  only  necessary  to  take  the  sun's  distance 
from  the  north  and  south  poles  respectively  at 
Greenwich  and  the  Cape  of  Good  Hope,  and  then 
subtracting  180°  from  the  sum  of  the  two  angular 
distances,  the  remainder  would  be  the  solar  parallax. 
The  difficulty  in  this  method  lies  in  the  fact  that 
when  the  sun  shines  the  air  is  full  of  tremulous  mo- 
tion. This  increases  refraction — that  plague  of  all 
astronomical  calculations — to  such  an  extent  that  it 
becomes  impossible  to  calculate  so  small  an  angle 
with  any  accuracy.  Neither  can  the  parallax  be 
estimated,  as  in  the  case  of  the  moon,  by  measuring 


Pig.  85. 


the  distance  from  a  fixed  star,  since  when  the  sun 
shines  the  stars  near  by  are  invisible  even  in  a  tele- 
scope. Astronomers  have  therefore  been  compelled 
to  resort  to  other  methods. 

(1.)  Calculation  of  solar  paraUax  by  observation  of 
the  planet  Mars. — We  have  already  seen  that  the  dis- 
tance of  Mars  from  the  sun  is  f  that  of  the  earth 
from  the  sun.  If,  therefore,  we  can  find  Mars'  dis- 
tance from  the  earth,  we  can  multiply  it  by  three, 


304  THE  SIDEREAL  SYSTEM. 

and  so  obtain  the  distance  of  the  sun  from  the  earth. 
In  1862,  when  Mars  was  in  opposition,  it  came  very 
near  us,  for  it  was  in  perihelion  while  the  earth  was 
in  aphelion,  so  that  its  distance  (as  since  ascertained) 
was  only  126,300,000  -  93,000,000  =  33,300,000  miles. 
Observers  at  Greenwich  and  the  Cape,  and  at  various 
American  and  European  observatories,  calculated 
the  distance  of  the  planet  from  the  north  and  south 
poles,  as  well  as  from  several  fixed  stars,  in  precisely 
the  manner  just  explained  for  obtaining  the  lunar 
parallax.  The  result  of  these  observations  fixed  the 
solar  parallax  at  8.94".* 

(2.)  Calculation  of  solar  paraUax  ty  observation  of 
the  transit  of  Femes. — In  the  figure,  let  A  and  B  rep- 
resent the  positions  of  two  observers  stationed  at 

Fig.  96. 


TRANSIT  OP  VENU8. 

opposite  sides  of  the  earth.  At  the  time  of  the 
transit,  the  one  at  A  will  see  the  planet  Venus  as  a 
round  black  spot  at  V"  on  the  sun's  disk,  while  the 
one  at  B  will  see  it  at  V.  The  distance  V'V"  is  the 

*  By  the  formula  on  page  302,  we  have — 

AS  :  AB  : :  Radius  :  Sin  8.94". 


CELESTIAL  MEASUREMENTS.  305 

difference  in  the  position  of  Venus  as  seen  from  the 
two  stations  on  the  earth.  The  distance  AB  is  the 
diameter  of  the  earth.  The  distance  VT"  is  as  much 
greater  than  AB  as  VV"  is  greater  than  VA.  The 
distance  of  Venus  from  the  sun  is  known,  by  Prob.  L, 
to  be  .72  that  of  the  earth.  The  distance  of  Venus 
from  the  earth  must  be,  then,  1.00  —  .72  =  .28. 
Hence,  W",  the  distance  from  the  sun  to  Venus,  = 
.72  -4-  .28=2.5  times  the  length  of  AV,  the  distance 
of  Venus  from  the  earth.  Therefore,  V'V"  is  equal 
to  2J  times  AB,  the  earth's  diameter,  or  5  times 
the  solar  parallax.  Knowing  the  hourly  motion  of 
Venus,  it  is  only  necessary  for  each  observer  to  find 
when  the  planet's  disk  enters  upon  and  leaves  the 
sun's  disk  to  determine  the  length  of  the  path  (chord) 
it  traces.  A  comparison  of  the  length  and  direction 
of  these  chords  will  give  the  length  of  V  V"  in 
seconds  of  space. 

The  advantage  of  this  method  is,  that  as  the  dis- 
tance V  V"  is  two  and  a  half  times  that  of  AB,  an 
error  in  measuring  that  chord  affects  the  solar  par- 
allax less  than  one-fifth. 

Time  of  a  transit  of  Venus. — This  is  an  event  of  rare 
occurrence.  It  happens  only  at  intervals  of  8,  105^ ; 
8, 121J,  years,  &c.  Were  the  planet's  orbit  in  the  same 
plane  as  the  ecliptic,  a  transit  would  take  place  dur- 
ing each  synodic  revolution ;  but  as  it  is  inclined 
about  3£°,  the  transit  can  occur  only  when  the  earth 
is  at  or  near  one  of  the  nodes  at  the  same  time  with 
the  planet,  when  in  inferior  conjunction.  As  the  nodes 


306  THE  SIDEREAL  SYSTEM. 

of  Yenus  fall  in  that  part  of  the  earth's  orbit  which 
we  pass  in  the  beginning  of  June  and  December 
transits  always  occur  in  those  months. 

The  transit  of  June  3d,  1769,  excited  great  interest. 
King  George  III.  fitted  out  an  expedition  to  Tahiti, 
under  the  command  of  the  celebrated  navigator  Capt. 
James  Cook.  In  order  to  make  the  angle  as  great 
as  possible,  and  so  increase  the  length  of  the  chords, 
or  paths  of  the  planet  across  the  sun,  astronomers 
were  sent  to  all  the  most  favorable  points  of  obser- 
vation— St.  Petersburg,  Pekin,  Lapland,  California, 
etc.  The  result  of  these  calculations  fixed  the  solar 
parallax  at  8.58".  This  was  considered  accurate  un- 
til lately,  but  has  now  ceased  to  have  any  value. 

The  next  transits  will  happen, 

December  8 ...  ...  1874. 


June          7 2004. 

The  first  transit  ever  seen  was  witnessed  by  Hor- 
rox,  a  young  amateur  astronomer  residing  near  Liv- 
erpool. His  calculations  fixed  upon  Sunday,  Nov. 
24, 1639  (O.  S.) 

He  however  commenced  his  watch  of  the  sun  on 
Saturday  preceding.  On  the  following  day  he  re- 
sumed his  observation  at  sunrise.  The  hour  for 
church  arriving,  Jie  repaired  to  service  as  usual.  Re- 
turning to  his  labor  immediately  afterward,  he  says : 
"  At  this  time  an  opening  in  the  clouds,  which  ren- 
dered the  sun  distinctly  visible,  seemed  as  if  Divine 
Providence  encouraged  my  aspirations;  when — oh 


CELESTIAL  MEASUREMENTS.  307 

most  gratifying  spectacle!  the  object  of  so  many 
earnest  wishes — I  perceived  a  new  spot  of  perfectly 
round  form  that  had  just  entered  upon  the  left  limb 
of  the  sun." 

The  transits  of  Mercury  are  more  frequent ;  but 
owing  to  the  nearness  of  the  planet  to  the  sun, 
they  are  of  little  value  in  determining  the  solar 
parallax. 

The  difficulty  of  determining  the  solar  parallax  accu- 
rately will  be  seen,  when  one  is  told  that  the  correc- 
tion from  the  old  value  of  8.58"  to  the  new  one  of 
8.94",  is  a  change  in  the  angle  equal  to  that  which 
the  breadth  of  a  human  hair  would  make  when  seen 
at  a  distance  of  125  feet.  Yet  this  reduces  the  esti- 
mated distance  of  the  sun  from  95,293,000  miles,  to 
91,430,000  miles. 

4.   TO  FIND   THE   LONGITUDE  OF  A  PLACE. — (1.)    The 

solar  method. — If  the  sailor  can  see  the  sun,  he 
watches  it  closely  with  his  sextant;  and  when  it 
ceases  to  rise  any  higher  in  the  heavens  it  is  appa- 
rent noon.  By  adding  or  subtracting  the  equation 
of  time  (as  given  in  his  almanac),  he  obtains  the  true 
or  mean  noon.  He  then  compares  the  local  time  thus 
obtained,  with  the  Greenwich  time  as  kept  by  the 
ship's  chronometer.  The  difference  in  time  reduced 
to  degrees,  etc.,  gives  the  longitude. 

(2.)  The  lunar  method. — On  account  of  the  difficulty 
in  obtaining  a  watch  which  will  keep  the  exact 
Greenwich  time  through  a  long  voyage,  the  moon  is 
more  generally  relied  upon  than  the  chronometer. 


308  THE  SIDEREAL  SYSTEM. 

The  Nautical  Almanac*  is  always  published,  for  the 
benefit  of  sailors,  three  years  in  advance.  It  gives 
the  distance  of  the  moon  from  the  principal  fixed 
stars  which  lie  along  its  path,  at  every  hour  in  the 
night.  The  sailor  has  only  to  determine  with  his 
sextant  the  moon's  distance  from  any  fixed  star,  and 
then  by  referring  to  his  almanac  find  the  correspond- 
ing Greenwich  time.  By  comparing  this  with  the 
local  time,  and  reducing  the  difference  to  degrees, 
etc.,  he  obtains  the  longitude. 

5.   TO    FIND    THE    LATITUDE    OF   A    PLACE. — (1.)    By 

means  of  the  sextant  find  the  elevation  of  the  pole 
above  the  horizon,  and  this  gives  the  latitude  di- 
rectly. (2.)  In  the  same  manner,  determine  the 
height  of  the  sun  above  the  horizon  at  noon.  The 
sun's  declination  for  that  day  (as  laid  down  in  the 
almanac),  added  to  or  subtracted  from  this  gives  the 
height  of  the  equinoctial  above  the  horizon.  Sub- 
tract this  from  90°,  and  the  remainder  is  the  lati- 
tude. 

*  It  is  pleasant  to  notice  that  the  astronomer  can  predict  with 
the  utmost  precision.  He  announces  that  on  such  a  year,  month, 
day,  hour,  and  second,  a  celestial  body  will  occupy  a  certain  posi- 
tion in  the  heavens.  At  the  tune  indicated  we  point  our  telescope 
to  the  place,  and  at  the  instant,  true  beyond  the  accuracy  of  any 
timepiece,  the  orb  sweeps  into  view !  A  prediction  of  the  Nauti- 
cal Almanac  is  received  with  as  much  confidence  as  if  it  were  a 
fact  contained  in  a  book  of  history.  "  On  the  trackless  ocean, 
this  book  is  the  mariner's  trusted  friend  and  counsellor;  daily  and 
nightly  its  revelations  bring  safety  to  ships  in  all  parts  of  the 
world.  It  is  something  more  than  a  mere  book.  It  is  an  ever- 
present  manifestation  of  the  order  and  harmony  of  the  universe.** 


CELESTIAL  MEASUREMENTS.  309 

6.  TO  FIND  THE  CIRCUMFERENCE  OF  THE  EARTH. — If 

the  earth  were  a  perfect  sphere,  it  is  obvious  that 
degrees  of  latitude  would  be  of  the  same  length  wher- 
ever measured  on  its  surface.  Each  would  be  -^ 
of  the  entire  circumference.  If,  however,  a  person 
sets  out  from  the  equator,  and  travels  along  a  me- 
ridian toward  either  pole,  and  when  the  polar  star 
has  risen  in  the  heavens  one  degree  above  the  ho- 
rizon, he  marks  the  spot,  and  then  continues  his 
journey,  marking  each  degree  in  succession,  he  will 
find  that  the  degrees  are  not  of  equal  length,  but 
increase  gradually  from  the  equator  to  the  pole.  If 
now  the  length  of  a  degree  be  measured  at  different 
places,  the  rate  of  variation  can  be  found,  and  then 
the  average  length  be  estimated.  Measurements  for 
this  purpose  have  been  made  in  Peru  (almost  exactly 
at  the  earth's  equator),  Lapland,  England,  France, 
India,  Russia,  etc.  So  great  accuracy  has  been  at- 
tained, that  Airy  and  Bessel,  who  have  solved  the 
problem  independently,  differ  in  their  estimate  of 
the  equatorial  diameter  but  77  yards,  or  only  yff^ 
of  a  mile. 

7.  To   FIND  THE  RELATIVE  SIZE  OF  THE  PLANETS. — 

The  volumes  of  two  globes  are  proportional  to  the 
cubes  of  their  like  dimensions.  The  diameter  of  Mer- 
cury is  2,962  miles,  and  that  of  the  earth  7,925 ;  then, 

The  volume  of  Mercury  :  the  volume  of  the  earth  : :  2962'  :  7925s. 

The  same  principle  applied  to  the  volume  or  bulk 
of  the  sun  gives — 

The  bulk  of  the  sun  :  bulk  of  earth  : :  852584'  :  7925*. 


310  THE  SIDEREAL  SYSTEM. 

8.   TO  FIND  THE  DIAMETER  OP  THE  SUN. — (1.)  A  Very 

simple  method  is  to  hold  up  a  circular  piece  of  paper 
before  the  eye  at  such  a  distance  as  to  exactly  hide 
the  entire  disk  of  the  sun.  Then  we  have  the  pro- 
portion, 

As  dist.  of  paper  disk  :  dist.  of  sun's  disk  ::  diam.  of  paper  d.  :  diam.  sun's  d. 

(2.)  The  apparent  diameter  of  the  sun,  as  seen 
from  the  earth,  is  about  32' :  the  apparent  diameter 
of  the  earth,  as  seen  from  the  sun,  is  twice  the  solar 
parallax,  or  17.88".  Thence,  the 

Ap.  diam.  of  earth  :  ap.  diam.  of  sun  : :  real  diam.  of  earth  :  real  diam.  of  sun. 

(3.)  Knowing  the  apparent  diameter  of  the  sun, 
and  its  distance  from  the  earth,  the  real  diameter  is 
found  by  Trigonometry.  In  figure  95,  let  S  repre- 
sent the  earth,  AB  the  radius  of  the  sun,  and  ASB 
half  the  apparent  diameter  of  the  sun.  We  shall 
then  have  the  proportion, 

AS  :  AB  : :  radius  :  sin.  16'  (half  mean  diam.  of  sun). 

By  a  similar  method  the  diameters  of  the  planets 
are  obtained. 

04  se 


APPENDIX. 


TABLE  ILLUSTRATING  KEPLER'S  THIRD  LAW.    (CHAMBERS.) 

IN  the  first  column  are  the  relative  distances  of 
the  planets  from  the  sun ;  in  the  second,  the  periodic 
times  of  the  planets ;  and  in  the  third,  the  squares 
of  the  periodic  times  divided  by  the  cubes  of  the 
mean  distances.  The  decimal  points  are  omitted  in 
the  third  column  for  convenience  of  comparison. 
The  want  of  exact  uniformity  is  doubtless  due  to 
errors  in  the  observations. 


Vulcan  ?  

.143 

19.7 

132  716 

Mercury  

.38710 

87969 

133  421 

Venus 

72333 

224  701 

133413 

Earth 

1 

365  256 

133408 

Mars  *..  . 

1.52369 

686.979 

133410 

Jupiter..  ... 

5.20277 

4  332  585 

133294 

Saturn 

9  53878 

10  759  220 

133401 

Uranus  

19.18239 

30,686.821 

133  422 

Neptune  

30.03680 

60,126.710 

133405 

Arago,  speaking  of  Kepler's  Laws,  says:  "These  interesting  laws,  tested 
for  every  planet,  have  been  found  so  perfectly  exact,  that  we  do  not  hesitate 
to  infer  the  distances  of  the  planets  from  the  sun  from  the  duration  of  their 
sidereal  periods ;  and  it  is  obvious  that  this  method  possesses  considerable 
advantages  in  point  of  exactness." 


MEASUREMENTS  OF  THE  EARTH'S  DIAMETER. 


Airy. 

Bessel. 

Polar  diameter  

7899.17 

7899.11 

Equatorial  diameter  . 

7925.64 

7925.60 

Compression 

26.47 

26.49 

g.3 

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QUESTIONS. 


THESE  are  the  questions  which  the  author  has  used  in  his 
own  classes  for  review  and  examination.  In  the  historical 
portion,  he  has  required  his  pupils  to  write  articles  upon  the 
character  and  life  of  the  various  persons  named,  gathering 
materials  from  every  attainable  source.  He  has  also  intro- 
duced whatever  problems  the  class  could  master,  taking  topics 
from  the  article  on  Celestial  Measurements  and  the  various 
mathematical  treatises. 

INTRODUCTION. — Define  Astronomy.  Is  the  earth  a  planet  ? 
What  is  the  difference  in  the  appearance  of  a  fixed  star  and 
a  planet?  What  is  the  Milky  Way?— HISTORY.  What  can 
you  say  of  the  antiquity  of  astronomy?  How  far  back  do 
the  Chinese  records  extend  ?  Name  some  astronomical  phe- 
nomena they  contain. 

17.  Why  should  the  Chaldeans  have  become  versed  in  this 
study?  How  ancient  are  their  records?  What  discoveries 
did  they  make  ?  What  Grecian  philosopher  early  acquired  a 
reputation  in  this  science  ?  What  other  discovery  did  Thales 
make  (Phil.,  p.  261)?  What  did -he  teach?  What  memora- 
ble eclipse  did  he  predict  ?  What  were  the  names  of  two  of 
his  pupils  ?  What  did  Anaximander  teach  ? 

IB.  Anaxagoras?  What  was  his  fate?  In  what  century 
did  Pythagoras  live  ?  What  was  his  characteristic  trait  ?  Did 
he  have  any  proof  of  his  system  ?  Explain  his  theory.  How 
does  it  differ  from  ours  ?  What  strange  views  did  he  hold  ? 
What  theory  did  Eudoxus  advance  ? 

19.  What  is  the  theory  of  the  crystalline  spheres?  What 
has  Hipparchus  been  styled?  What  addition  did  he  make 
to  astronomical  knowledge  ?  How  many  stars  in  our  present 
catalogue  (p.  228)  ?  How  did  Egypt  rank  in  science  at  an 
early  day?  What  preparation  did  the  Grecian  philosophers 
make  to  fit  themselves  for  teachers  ?  How  long  did  Pythag- 
oras travel  for  this  purpose  ?  What  can  you  say  of  the  school 
at  Alexandria?  What  great  work  did  Ptolemy  write  there? 
What  theory  did  he  expound  ? 


316  QUESTIONS  IN  ASTRONOMY. 

20.  Was  it  original  ?     What  discovery  did   Eratosthenes 
make?     Describe   that   method    (p.  309).       Show  how  the 
movements  of  the  planets  puzzled  the  ancients.     What  was 
the  theory  of  " cycles  and  epicycles?" 

21.  Did  the  ancients  believe  in  the  reality  of  this  cumbrous 
machinery?     Did  this  theory  possess  any  accuracy?     Could 
they  adapt  it  to  explain  any  new  motion  ? 

22.  What  was  the  remark  of  Alphonso  ?     When  did  astron- 
omy cease  to  be  cultivated  as  a  science  ?     In  what  century  ? 
Why  did  Caesar  import  an  astronomer  ?     Why  did  he  attempt 
to  revise  the  Calendar  ?     What  change  did  he  make  (p.  295)  ? 
State  something  of  the  repute  in  which  astrology  was  held. 

23.  Tell  what  you  can  of  the  system.     What  use  did  it  sub- 
serve?     What    theory   displaced    the   Ptolemaic?      When? 
Was  the  system  of  Copernicus  original  ?     What  credit  is  due 
him  ?     Describe  his  idea  of  apparent  motion.     How  did  he 
apply  this  to  the  heavenly  bodies  ? 

24.  What  crudity  did  he  retain  ?     Who  was  Tycho  Brahe  ? 
What  was  his  theory?     How  did  it  differ  from  Ptolemy's  and 
Copernicus's  ? 

25.  What  good  did  he  accomplish?     Could  he  generalize 
hisf  facts  ?     Had  he  a  telescope  ?     How  did  Kepler  differ  from 
Brahe  ?     What  were  the  two  prominent  characteristics  of  Kep- 
ler ?     Give  his  three  laws.     Tell  how  he  discovered  the  first. 
The  second.     The  third  (p.  313).     Describe  the  ellipse.     De- 
fine focus,  perihelion,  and  aphelion.     What  remarkable  state- 
ment did  Kepler  make  ? 

29.  When  did  Galileo  live  ?     What  discoveries  did  he  make 
in   Natural   Philosophy?  .In  Astronomy?     What  advantage 
did  he  have  over  his  predecessors  ? 

30.  Give  an  account  of  his  observations  on  the  moon.     On 
Jupiter's  moons. 

31.  Why  did  this  settle  the  controversy  between  the  Ptole- 
maic and  the  Copernican  system?     How  were  Galileo's  dis- 
coveries received  ?    Give  some  of  Sizzi's  ponderous  arguments. 

33.  Who  discovered  the  law  of  gravitation  ?  Repeat  it. 
How  was  this  idea  suggested  ?  What  familiar  laws  of  motion 
aided  Newton  ?  How  did  he  apply  these  to  the  motion  of  the 
moon  ?  Repeat  the  story  of  his  patient  triumph. 

35.  What  is  the  celestial  sphere?    Give  the  two  illustrations 
which  show  its  vast  distance  from  the  earth. 

36.  Why  can  we  not  see  the  stars  by  day,  as  by  night? 
What  portion  of  the  sphere  is  visible  to  us  ?     Name  the  three 
systems  of  circles. 

37-41.  Name  and  define  (i)  the  principal   circle,  (2)  the 


QUESTIONS  IN  ASTRONOMY.  317 

secondary  circles,  (3)  the  points,  and  (4)  the  measurements 
of  each  system.  Define,  especially,  because  in  common  use, 
zenith,  nadir,  azimuth,  altitude,  equinoctial,  right  ascension, 
declination,  equinox,  ecliptic,  colure,  and  solstice.  What  is  N 
or  S  in  the  heavens  ?  What  is  the  Zodiac  ? 

42.  How  wide?  How  ancient?  How  divided?  Give  the 
names  and  signs.  State  the  meaning  of  each  (p.  229). 

II.  THE  SOLAR  SYSTEM. 

Of  what  is  the  solar  system  composed  ?  Describe  how  we 
are  to  picture  it  to  ourselves. 

THE  SUN. — Its  sign.     Its  distance  from  us  ?    Illustrate. 

47.  How  are  celestial  distances  measured  ?  To  what  is  the 
sun's  light  equal  ?  To  how  many  full  moons  ?  Its  heat?  Illus- 
trate. What  proportion  of  the  sun's  heat  reaches  the  earth  ? 

48-50.  Its  apparent  size  ?  How  does  this  vary  ?  Its  dimen- 
sions— (i)  diameter — illustrate,  (2)  volume,  (3)  mass,  (4) 
weight,  (5)  density.  How  large  did  Pythagoras  think  the  sun 
is  ?  Tell  something  about  the  force  of  gravity  in  the  sun. 
How  much  would  you  weigh  if  carried  to  its  surface?  (This 
can  be  calculated  from  the  table  in  Appendix.)  How  does  the 
sun  appear  to  the  naked  eye  ?  How  can  we  see  the  spots  ? 
What  were  formerly  the  views  of  astronomers  with  regard  to 
the  sun's  face  ?  When  were  the  spots  discovered  ? 

52.  Tell  something  about  the  number  of  the  spots.     Their 
location.     Size. 

53.  Describe  the  parts  of  which  they  are  composed.     The 
motion  of  the  spots. 

54-5.  How  do  they  change  in  form  as  they  pass  across  the 
disk  ?  What  does  this  prove  ?  What  is  the  length  of  a  solar 
axial  revolution  ?  Explain  a  sidereal  and  a  synodic  revolution. 

56-7.  Why  do  not  the  spots  move  in  straight  lines?  Show 
how  they  curve.  Tell  what  you  can  about  the  irregular  move- 
ments of  the  spots.  Tell  how  suddenly  they  change. 

58.  What  can  you  say  about  their  periodicity?     Who  dis- 
covered this  ?    Is  there  any  connection  between  the  solar  spots 
and  the  aurora?    Tell  the  influence  of  the  planets  on  the  spots. 
Explain. 

59.  Do  the  spots  affect  the  fruitfulness  of  the  season  ?    Does 
the  temperature  of  the  spots  differ  from  that  of  the  rest  of  the 
sun  ?     Are  they  depressions  in  the  sun  ?     How  much  darker 
are  they  than  the  adjacent  surface  ? 

60.  Is  the  sun  brighter  than  the  Drummond  light?    Ans. 
The  sun  gives  out  as  much  light  as  one  hundred  and  forty-six 


318  QUESTIONS  IN  ASTRONOMY. 

lime-lights  would  do,  if  each  were  as  large  as  the  sun  and 
were  burning  all  over.  What  are  the  faculae  ?  Describe  the 
mottled  appearance  of  the  sun. 

61.  What  is  the  shape  of  the  bright  masses?    What  is  a 
pore? 

62.  Describe  the  constitution  of  the  sun  according  to  Wil- 
son's theory.     How  are  the  spots  produced  ?     The  faculae  ? 

63.  The  penumbra?     The  umbra? 

64.  What  is  KirchhofFs  theory?     How  are  the  spots  pro- 
duced?     The  umbra?      The  penumbra?     Upon  what  does 
this  theory  depend  (p.   286)  ?      What  is    the  cause  of  the 
heat  of  the  sun  ?    Will  the  heat  ever  cease  ?  * 

THE  PLANETS. — Name  the  six  characteristics  common  to 
all  the  planets. 

67.  Compare  the  two  groups  of  the  major  planets. 

68.  Draw  an  ellipse,  and  name  the  various  parts.     Define 
the  ecliptic,  f     The  ascending  node.     The  descending  node. 
Line  of  the  nodes.     Longitude  of  the  node.     Tell  what  you 
can  with  regard  to  the  comparative  size  of  the  planets. 

71.  What  is  a  conjunction  ?    Name  the  earliest  that  are  re- 
corded. 

72.  Tell  what  you  can  concerning  the  planets  being  in- 
habited. 

74.  What  about  the   conditions   of  life   on  the   different 
planets  ?     What  are  the  two  divisions  of  the  planets  ? 

75.  What  causes  the  apparently  irregular  movements  of 
the  planets  ?     Define  heliocentric  and  geocentric  place.     Il- 
lustrate.    In  what  part  of  the  sky  is  an  inferior  planet  always 
seen  ?     Define  inferior  and  superior  conjunction. 

76.  Greatest  elongation.     Quadrature.     Why  is  a  star  at 
one  time  "  evening"  and  at  another  "  morning  star?" 

77.  What  is  a  transit  ?     Explain  the  retrograde  motion  of 
an  inferior  planet.     (This  motion,  it  will  be  remembered,  was 
one  that  sorely  puzzled  the  ancients. ) 

*If  we  accept  the  Nebular  hypothesis  (p.  283),  we  must  suppose  that 
the  heat  is  produced  by  the  condensation  of  the  nebulous  matter  and  con- 
sequent chemical  changes.  The  sun  is  radiating  its  heat  constantly,  and, 
after  a  time,  will  go  out,  in  turn,  as  the  earth  and  all  the  planets  have  be- 
fore it. 

j- Lockyer  beautifully  says  :  "We  may  imagine  the  earth  floating  around 
the  sun  on  a  boundless  ocean,  both  sun  and  earth  being  half  immersed  in  it. 
This  level,  this  plane,  the  plane  of  the  ecliptic  (because  all  eclipses  occur 
in  it),  is  used  by  astronomers  as  we  use  the  sea-level.  We  say  a  moun- 
tain is  so  far  above  the  level  of  the  sea.  The  astronomer  says  a  star  is  so 
high  above  the  level  of  the  ecliptic." 


QUESTIONS  IN  ASTRONOMY.  319 

78.  Describe  the  phases  of  an  inferior  planet.     Why  does 
an  inferior  planet  have  phases  ?    Define  gibbous. 

79.  Explain  the  opposition  and  conjunction  of  a  superior 
planet.     Its  retrograde  motion.     Must  a  superior  planet  al- 
ways be  seen  in  the  same  part  of  the  sky  as  the  sun  ? 

80.  Which  retrogrades  more,  a  near  or  a  distant  planet? 
Define  a  sidereal  and  a  synodic  revolution  of  an  inferior  and  a 
superior  planet,  and  tell  what  you  can  about  each.     In  what 
case  would  there  be  no  difference  between  a  sidereal  and  a 
synodic  revolution  ?    Why  is  a  planet  invisible  when  in  con- 
junction ? 

82.  When  is  a  planet  evening,  and  when   morning  star  ? 
Tell  what  you  can  about  the  supposed  discovery  of  a  planet 
interior  to  Mercury. 

83.  MERCURY. — Definition  and  sign  ?  Describe  the  appear- 
ance of  Mercury,  and  where  seen. 

84.  What  was  the  opinion  of  the  ancients  ?    The  astrolo- 
gists  ?    Chemists  ?    Why  is  it  difficult  to  see  it  ?    When  can 
we  see  it  best  ? 

85.  What  is  the  peculiarity  of  its  orbit  ?     Its  distance  from 
the  sun?    Velocity?    Length  of  its  day?    Year?    Difference 
between  its  sidereal  and  synodic  revolution  ?  why  ?     Its  dis- 
tance from  the  earth  ? 

86.  Show  why  its  greatest  and  least  distances  vary  so  much. 
What  is   its    diameter  ?      Volume  ?      Density  ?      Force  of 
gravity?     Specific  gravity  ?     How  much  would  you  weigh  on 
Mercury?     Describe  its  seasons.     (If  the  pupil  does  not  un- 
derstand pretty  well  the  subject  of  the  terrestrial  seasons,  it 
would  be  well  here  to  read  carefully  page  no,  et  seq.) 

88.  Its  temperature  ?    Appearance  of  the  sun  ?    Has  it  any 
moon?     What  is  the  appearance  of  the  planet  through  a 
telescope  ?    What  do  these  phases  prove  ?    What  do  we  know 
of  its  mountains  and  valleys  ? 

89.  VENUS. — Definition  and  sign  ?    Ancient  names  ?    Ap- 
pearance to  us  ? 

90.  When  brightest?    Can  Venus  be  seen  by  day?     Il- 
lustrate. 

91.  Describe  the  orbit.      What  is  the  distance  of  Venus 
from  the  sun  ?    Velocity?    Length  of  the  year?    Day?     Dif- 
ference between  the  sidereal  and  synodic  revolution?    Dis- 
tance from  the  earth  ? 

92.  How  does  the  apparent  size  vary  ?    When  is  Venus  the 
brightest?     What  is  the  diameter ?    Volume?    Density? 

93.  Force  of  gravity?    Does  the  force  of  gravity  increase 


320  QUESTIONS  IN  ASTRONOMY. 

or  decrease  with  the  mass  or  volume  of  the  body  ?    Describe 
the  seasons. 

94.  Describe  the  telescopic  appearance.     Who  discovered 
the  phases  of  Venus  ?     What  was  Copernicus's  idea  ? 

95.  What  proof  have  we  of  an  atmosphere?     Of  clouds? 
Has  Venus  any  moon  ? 

96.  EARTH. — Sign  ?    What  is  the  appearance  of  the  earth 
from  the  other  planets?    Do  we,  then,  live  on  a  star?     Is  it 
probable  that  the  earth  was  always  dark  and  dull  as  it  now 
seems  to  us  ?  *     How  does  the  size  of  the  earth  compare  with 
that  of  the  other  planets  ?     Form  of  the  earth  ?    Exact  diam- 
eter ?     Is  the  equator  a  perfect  circle  ? 

98.  Circumference  ?    Density  ?    Weight  ?    What  can  you 
say  of  its  inequalities  ?    How  do  you  prove  the  rotundity  of 
the  earth  ? 

99.  Why  can  we  see  further  from  the  top  of  a  hill  than 
from  its  base  ?    Why  is  the  horizon  a  circle  ? 

100.  Give  some  illustrations  of  apparent  motion. 

101.  Explain  the  cause  of  the  rising  and  setting  of  the  sun 
and  stars.     Who  first  explained  it  in  this  manner  ?     What  do 
you  say  of  its  simplicity  ? 

1 02.  Cause  of  day  and  night?    Do  all  places  on  the  earth 
revolve  with  equal  velocity  ?    Illustrate.    At  what  rate  do  we 
move? 

103.  Why  do  we  not  perceive  our  motion  ?     What  would 
be  the  effect  if  the  earth  were  to  stop  ? 

104-5.  Is  there  any  danger  of  this  catastrophe  ?  Draw  the 
figure,  and  show  how  the  stars  move  daily  through  unequal 
orbits  and  with  unequal  velocities.  Describe  the  appearance 
of  the  stars  at  the  N.  Pole. 

1 06.  At  the  Equator.     S.  Pole.     Describe  the  path  of  the 
earth  about  the  sun.     Define  eccentricity.     Is  this  stable  ? 

107.  Do  we  see  the  same  stars  at  different  seasons  of  the 
year?    Why  not?    If  we  should  watch  from  6  P.  M.  to  6  A.  M., 
what  portion  of  the  sphere    could  we   see?     What  do  we 
mean  by  the  yearly  motion  of  the  sun  among  the  stars?    How 
can  we  see  it  ? 

109.  What  is  the  cause?  What  is  the  ecliptic?  Why  so 
called  ?  What  are  the  equinoxes  ?  What  do  we  understand 

*  Probably  not.  The  earth  was  doubtless  once  a  glowing  star,  like  the 
sun.  Its  crust  is  only  the  ashes  and  cinders  of  that  fearful  conflagration. 
The  rocks  are  all  burnt  bodies.  The  atmosphere  is  only  the  gas  left  over 
after  the  fuel  was  all  consumed.  Every  organic  object  has  been  rescued  by 
plants  and  the  sunbeam  from  the  grasp  of  oxygen. 


QUESTIONS  IN  ASTRONOMY.  321 

when  we  see  in  the  almanac  "the  earth  is  in  Aries?"     "The 
sun  is  in  Sagittarius  ?" 

1 10.  How  many  apparent  motions  has  the  sun  ?  Name 
them,  and  give  the  cause  and  effects  of  each.  Has  the  sun  any 
real  motions  (pp.  54  and  224)  ?  Describe  the  apparent  mo- 
tion of  the  sun,  N.  and  S.  How  is  it  that  the  sun  in  summer 
shines  on  the  north  side  of  some  houses  both  at  rising  and 
setting,  but  in  winter  never  does?  Define  the  obliquity  of  the 
ecliptic.  The  parallelism  of  the  earth's  axis.  What  do  you 
say  of  its  permanence  ? 

112.  Why  will  a  top  stand  while  spinning,  but  will  fall  as  soon 
as  it  ceases  ?     Show  how  the  rays  of  the  sun  strike  the  various 
parts  of  the  earth  at  different  angles  at  the  same  time.     Show 
how  the  angles  vary  at  different  times.     Is  the  sun  really  hotter 
in  summer  than  in  winter  ?     Why  does  it  seem  to  be  ? 

113.  Explain  the  cause   of   equal   day  and  night  at  the 
Equinoxes.     Why  are  our  days  and  nights  of  unequal  length 
at  all  other  times  ?     Why  do  they  vary  at  different  seasons  of 
the  year  ?     How  do  the  seasons,  &c. ,  in  the  N.   Temperate 
Zone  compare  with  those  in  the  S.  Temperate  Zone  ?     De- 
scribe the  yearly  path  of  the  earth  about  the  sun — ( i )  at  the 
summer  solstice ;    (2)  at  the  autumnal  equinox;    (3)  at  the 
winter  solstice  ;   (4)  at  the  vernal  equinox ;   (5)  the  yearly  path 
finished  back  to  the  starting-point.      Is  the  division  of  the 
earth's  surface  into  zones  an  artificial  or  a  natural  distinction  ? 
Who  invented  it  ? 

117.  How  much  nearer  are  we  to  the  sun  in  the  winter? 
Why  is  it  not  the  warmest  at  that  time  ?     How  is  it  in  the 
South  Temperate  Zone  ?     When  do  the  extremes  of  heat  and 
cold  occur  ?     Why  not  exactly  at  the  solstices  ? 

1 1 8.  Why  is  summer  longer  than  winter?     Does  the  earth 
move  with  the  same  velocity  in  all  parts  of  its  orbit  ?     Describe 
the  curious  appearance  of  the  sun  at  the  North  Pole.      In 
Greenland,  at  what  part  of  the  year  will  the  midnight  sun  be 
seen  due  north  ?     What  is  the  length  of  the  days  and  nights 
at  the  Equator  ? 

119.  Describe  the  results  if  the  axis  of  the  earth  were  per 
pendicular  to  the  ecliptic. 

120.  If  the  equator  were  perpendicular  to  the  ecliptic.    De- 
fine precession  of  the  equinoxes.     Who  discovered  this  ?     At 
what  rate  does  this  movement  proceed  ?     What  is  the  amount 
at  present  ? 

121.  What  are  the  results?     What  star  was  formerly  the 
Pole  star  ? 

123.  Explain  the  cause  of  precession. 


322  QUESTIONS  IN  ASTRONOMY. 

125.  How  does  the  spinning  of  a  top  illustrate  this  subject? 

126.  What   is  Nutation?     Cause?     How  does  the  moon's 
influence  compare  with  that  of  the  sun  ? 

127.  What  is  the  real  path  of  the  N.   Pole  through  the 
heavens  ?     Is  the  obliquity  of  the  ecliptic  invariable  ?     What 
is  the  limit  ?     What  is  the  effect  of  this  variation  ? 

128.  Are  the  solstices  and  equinoxes  stationary?     What  is 
the  result  of  this  change  on  the   seasons  ?      When  will   the 
cycle  be  completed  ?     When  is  the  sun  in  perigee  ? 

129.  What  do  you  say  of  the  provisions  made  to  secure 
permanence,  so  that  slight  changes  themselves  prevent  greater 
changes  ? 

130.  What  is  refraction?     Its  effect? 

131.  How  does  it  vary? 

132.  Are  the  sun  and  moon  ever  where  they  seem  to  be  ? 
Is  the  real  day  longer   or  shorter   than  the   apparent  one  ? 
Why  do  the  sun  and  moon  appear  flattened  when   near  the 
horizon  ?     Why  not  when   they  are   high   in   the   heavens  ? 
Why  do  they  appear  smaller  in  the  latter  case  ? 

133.  What  causes  the  hazy   appearance   of   the  heavenly 
bodies  near  the  horizon?      What  is  the  cause  of  twilight? 
How  long  does  it  last  ?     Is  it  the  same  at  all  seasons  of  the 
year? 

134.  At  all  parts   of   the   earth?      Where   is   it  longest? 
Shortest  ?     What  is  diffused  light  ?     What  would  be  the  effect 
if  the  atmosphere  did  not  act  in  this  way  ?r    Is  there  really  any 
sky  in  the  heavens  ?     Cause  of  the  appearance  ? 

135.  What  is  aberration  of  light  ?      Illustrate.      Give  two 
reasons  why  we  never  see  the  sun  where  it  really  is. 

137.  The  general  effect  of  aberration  ?      Define   parallax. 
Illustrate. 

138.  Define  true  and  apparent  place.      How  does  parallax 
vary  ?     What  is  the  practical  importance  of  this  subject  (p. 
300,  etseq.)? 

139.  Define  horizontal  parallax.     What  is  the  sun's  hori- 
zontal parallax  ?     What  is  the  annual  parallax  ? 

THE  MOON. — Signs  ?     Describe  its  orbit. 

140.  Its  distance  from  the  earth  ?     Illustrate.      Difference 
between  its  sidereal  and  synodic  revolution  ? 

141.  What  is  the  real  path  of  the  moon?     (Imagine  a  pen- 
cil fastened  to  the  spoke  of  a  wheel,  and  the  wheel  rolled  by 
the  side  of  a  wall  on  which  the  pencil  is  constantly  marking. ) 
How  often  does  it  turn  on  its  axis  ?     What  is  the  moon's  di- 
ameter ?     Volume  ?     How  does  its  apparent  size  vary  ?     Why 
does  it  appear  larger  than  it  really  is  ? 


QUESTIONS  IN  ASTRONOMY.  323 

142.  Why  does  the  crescent  moon  appear  larger  than  the 
dark  body  of  the  moon  ?     When  ought  the  moon  to  appear 
the  largest  ?     Do  all  persons  think  the  moon  of  the  same  ap- 
parent size  ?     Explain  the  three  librations  of  the  moon. 

143.  How  does  moonlight  compare  with  sunlight  ?    Is  there 
any  heat  in  moonlight  ?      Why  is  it   generally  clear  at  full 
moon  ?     Does  the  centre  of  gravity  in  the  moon  coincide  with 
that  of  magnitude  ?     Has  the  moon  any  atmosphere  ?     What 
proof  have  we  of  this? — Ans.  (i)  We  see  but  slightly  if  any 
appearance  of  twilight  in  the  moon.    (2)    When  the  moon 
passes  between  us  and  a  star,  it  does  not  refract  the  light  of 
the  star,  so  that  the  atmosphere  cannot  be  sufficient  to  sup- 
port more  than  TOTT  of  an  inch  of  the  mercurial  column. 

144.  How  does  the  earth  appear  from  the  moon  ?    What  is 
the  earth-shine ?     How  is  it  caused?      What  is  it  called  in 
England  ?     Describe  the  path  of  the  moon  around  the  earth, 
and  the  consequent  phases.     Why  is  new  moon  seen  in  the 
west  and  full  moon  in  the  east  ?    Why  can  we  sometimes  see 
the  moon  in  the  west  after  the  sun  rises,  and  in  the  east  before 
the  sun  sets  ? 

147.  Length  of  a  lunar  month  ?    What  do  we  mean  by  the 
moon's  running  high  or  low  ?     Cause  ?     Use  ? 

148.  What  is  harvest  moon?     Hunter's  moon?     Cause? 

149.  What  are  nodes  ?     How  much  is  the  moon's  orbit  in- 
clined to  the  ecliptic— our  ideal  sea-level  ?     What  is  an  oc- 
cultation?     Use? 

150.  Describe  the  seasons,  heat,  &c.,  on  the  moon. 

152.  Telescopic  appearance  of  the  moon  ?  Are  the  mount- 
ains the  light  or  dark  portions  ?  What  can  you  say  about 
them  ?  The  gray  plains  ?  The  rills  ?  The  craters  ?  What 
are  the  peculiar  features,  then,  of  the  lunar  landscapes  ?  Are 
the  lunar  volcanoes  extinct  ? 

ECLIPSES. — When  can  an  eclipse  of  the  sun  occur?  Show 
how  a  solar  eclipse  may  be  total,  partial,  or  annular. 

156.  Define  umbra.  Penumbra.  Central  eclipse.  State 
the  general  principles  of  a  solar  eclipse. 

158.  What  curious  phenomena  attend  a  total  eclipse? 

159.  Describe  the  effect  of  a  total  eclipse? 

1 60.  What  curious  custom  prevails  among  the  Hindoos? 
What  is  the  Saros  ?     Cause  ? 

161.  Is  it  now  of  any  value?     What  is  the  metonic  cycle? 
Explain  its  use. 

162.  What  is   the   golden   number?      Cause   of   a  lunar 
eclipse  ?     Draw  the  figure  and  describe  it.      Why  are  lunar 
eclipses  seen  oTtener  than  solar  ones  ? 


324  QUESTIONS  IN  ASTBONOMY. 

163.  What  is  the  earliest  account  of  an  eclipse  ?     How  were 
eclipses  formerly  regarded  ? 

164.  What  story  is  told  of  Columbus  ? 

THE  TIDES.*— Define  ebb.  Flow.  How  often  does  the 
tide  happen  ?  Explain  the  cause. 

1 66.  Why  does  the  tide    occur  fifty  minutes  later  each 
day  ?     Why  is  there  a  tide  on  the  side  opposite  the  moon  ? 
The  sun  is  much  larger  than  the  moon  ;  why  does  it  not  pro- 
duce the  larger  tide  ?    Why  is  not  the  tide  felt  out  at  sea  ? 

167.  What  is  spring-tide?      Neap-tide?     Causes?     Why 
does  the  tide  differ  so  much  in  various  localities  ?     Tell  about 
the  height  of  the  tide  at  different  points. 

1 68.  Why  is  there  no  tide  on  a  lake  ? 
MARS. — Definition  and  sign  ? 

169.  Describe  its  appearance.      When  is  it  brightest  ?     Its 
distance  from  the  sun  ?     Velocity  ?     Day  ?     Year  ? 

170.  Distance  from  the  earth?      Peculiarity  of  its  orbit? 
Diameter?      Volume?      Density?     Mass?     Force  of  gravity? 
Figure  ?    Describe  its  seasons. 

171.  Has  it  any  atmosphere?      Moon?      Appearance   of 
our  earth  ?     Telescopic  features.     (The  land  and  sea  features 
have  been  so  well  decided  that  they  have  been  named,  and  a 
Mars's  globe  made.) 

172.  Cause  of  its  ruddy  color ?    What  are  the  snow-zones? 
Can  we  watch  the  change  of  its  seasons  ? 

MINOR  PLANETS  (ASTEROIDS). — Give  Bode's  law.  Tell 
how  the  first  of  these  planets  was  discovered.  How  many  are 
now  known? — Ans.  There  are  (Sept.  21,1870)112.  Are  they 
probably  all  discovered  ? 

174.  Describe  these  "pocket  planets."  Are  they  all  found 
within  the  Zodiac?  What  is  their  origin? — Ans.  According 
to  the  Nebular  hypothesis,  the  ring  of  matter  broke  up  into 
numberless  small  bodies  instead  of  aggregating  into  one  large 
planet.  Give  some  of  the  names  and  signs. 

JUPITER. — Definition  and  sign  ?  Describe  its  appearance. 
Ancient  views.  Describe  its  orbit.  What  is  its  distance  from 
the  sun?  Velocity?  (1869.  n  is  in  r).  Day?  Year?  Dis- 
tance from  the  earth  ? 

177.  Diameter?    Volume?     Density?     Centrifugal  force? 

*.  As  the  tidal  wave  does  not  move  as  rapidly  as  the  earth  does,  the 
water  has  an  apparent  backward  motion.  It  has  been  suggested  that  this 
acts  as  a  ^reak  on  the  earth's  diurnal  revolution.  It  has  been  shown  that 
the  moon's  true  place  can  be  best  calculated  if  we  suppose  that  the  sidereal 
day  is  shortening,  by  tidal  action,  at  the  rate  of  •£%  of  a  second  in  2,500 
years. 


QUESTIONS  IN  ASTRONOMY.  325 

Force  of  gravity  ?  Figure  ?  Describe  its  seasons.  Upon  what 
does  the  change  of  seasons  in  any  planet  depend  ? 

178.  The  appearance  of  the  sky  ?     The  telescopic  features? 
Are  Jupiter's  moons  visible  to  the  naked  eye  ? 

179.  How  named?     What  is  their  size?     What  space  do 
they  occupy  ? 

1 80.  Describe  the  eclipse  of  the  moons. 

181.  Define  immersion,  emersion,  and  transit.     How  rapid- 
ly do  the  satellites  revolve  ?     What  can  you  say  of  the  fre- 
quency of  eclipses  on  Jupiter  ?    Describe  the  belts.     Why  are 
they  parallel  to  its  equator  ? 

182.  How  was  the  velocity  of  light  discovered  ? 
SATURN. — Definition  and  sign  ?    Describe  its  appearance. 

How  rapidly  does  it  move  through  the  sky?  (1869.  »  is  in  m). 
Its  distance  from  the  sun  ?  Peculiarity  of  its  orbit  ? 

184.  Velocity?     Year?     Day?     Distance  from  the  earth? 
Diameter?     Volume?     Density?      Force  of  gravity?     De- 
scribe its  seasons. 

185.  Has  it  any  atmosphere?     Who  discovered  the  rings 
of  Saturn  ?     Describe  them. 

1 86.  Are  they  stationary?     Explain  their  phases. 

187.  Describe  Saturn's  belts. 

1 88.  Describe  Saturn's  moons.     The  scenery  on  Saturn. 
URANUS. — Definition  and  sign ?     How  was  it  discovered? 

Tell  of  its  previous  discovery  by  Le  Monnier.  Is  Uranus 
visible  to  the  naked  eye  ?  (1869.  Jjt  is  in  o).  Distance  from 
the  sun?  Year?  Diameter?  Density? 

191.  Describe  its  seasons.     Telescopic  features.    Satellites 
Peculiarity  of  its  moons. 

NEPTUNE. — Definition  and  sign  ?  Appearance  in  the  sky? 
Give  an  account  of  its  wonderful  discovery. 

193.  What  is  its  distance  from  the  sun  ?    Year  ?    Velocity  ? 
Diameter?     Volume?     Density?     Do  we  know  anything  of 
the  seasons  ?     Why  not  ?     Intensity  of  the  light  ? 

194.  Appearance  of  the  heavens  ?    What  are  the  telescopic 
features  ?     Has  Neptune  any  moon  ?     What  advantage  have 
the  Neptunian  astronomers? 

METEORS,  AEROLITES,  AND  SHOOTING-STARS. — Define  an 
aerolite.  A  shooting-star.  A  meteor.  Give  some  account 
of  the  fall  of  meteors  (aerolites). 

197.  What  elements  are  found  in  aerolites?      How  can  an 
aerolite  be  distinguished  ?      Give  an   account  of  wonderful 
meteors. 

198.  Of  shooting-stars. 

199.  Describe  the  showers  of  1799  and  1833. 


326  QUESTIONS  IN  ASTRONOMY. 

200.  The  shower  of  1866.     At  what  intervals  did  these  showers 
occur?    Why  was  not  the  shower  of  1866  seen  in  this  country t 
Am.  Our  side  of  the  earth  was  not  turned  toward  the  meteors. 

201.  What  is  the  average  number  of  meteors  and  shooting- 
stars  daily  ?    Why  do  we  not  see  more  of  them  ? 

202.  In  what  months  are  they  most  abundant?    Describe 
the  origin  of  meteors  and  shooting-stars.       What  is  their 
velocity  ?     What  causes  the  light  ?      The  explosion    often 
heard  ?    What  is  said  of  a  companion  to  our  moon  ? 

203.  What  is  the  theory  of  meteoric  rings  ?    What  is  their 
shape  ?     How  do  these  account  for  the  showers  at  regular  in 
tervals  ? 

204.  What  is  the  period  of  the  November  ring  ?    Why  is 
the  August  shower  so  uniform,  while  the  November  one  is  only 
periodic  ? 

205.  What  is  the  relation  between  meteors  and  comets? 
What  do  you  mean  by  the  radiant  point  ?     What  effect  do 
meteors  have  on  the  weather  ? 

206.  What  is  their  height  ?     Weight  ? 

COMETS. — How  were  they  looked  upon  by  the  ancients  ?  Il- 
lustrate. Define  the  term  comet.  What  is  the  tail  ?  The 
nucleus  ?  The  head  ?  The  coma  ?  Does  each  comet  neces- 
sarily possess  all  these  parts  ?  How  would  a  mere  round, 
fleecy  mass  be  known  to  be  a  comet  ?  What  mistake  did 
Herschel  make  in  looking,  as  he  supposed,  at  one  of  this 
kind  (p.  189)? 

208.  Where  do  comets  appear  ?     In  what  direction  do  they 
move  ? .   How  does  a  comet  look  when  first  seen  ?     Upon  what 
does  the  time  of  greatest  brilliancy  depend  ?    What  do  you  say 
of  the  number  of  the  comets  ?    What  was  Kepler's  remark  ? 

209.  Why  do  we  not  see  them  oftener  ?    Where  did  Seneca 
see  one?     Describe  the  orbits  of  comets.     Which  class  has 
been  calculated  ?     Which  classes  never  return  ? 

210.  Describe  the  difficulty  of  calculating  a  comet's  orbit. 

211.  Name  the  periods  of  some.     What  has  been  the  dis- 
tance from  the  sun  of  some  noted  comets  ?     Velocity  ? 

212.  What  do  you  say  of  the  density  of  a  comet  ?    Illustrate. 
Is  there  any  danger  of  our  running  against  a  comet? 

213.  Do  comets  shine  by  their  own  or  by  reflected  light? 
Tell  what  you  can  of  their  variation  in  form  and  dimensions. 

214.  Give  some  account  of  the  comets  of  1811,   1835,  and 
1843.     For  what  is  Encke's  comet  noted  ?     What  is  its  period? 
Give  some  description  of  Donati's  comet. 

ZODIACAL  LIGHT.— Where  can  this  be  seen?  What  is  its 
appearance  ?  Where  is  it  brightest  ?  What  is  its  origin  ? 


QUESTIONS    IN   ASTRONOMY.  327 


III. — THE  SIDEREAL   SYSTEM. 

Tell  something  of  the  appearance  of  the  heavens  at  Nep- 
tune's distance  from  the  sun — our  starting-point?  Do  we 
ever  see  the  stars  ?  What  do  we  see,  then  ? 

222.  Which  star  is  nearest  the  earth  ?     What  is  its  paral- 
lax?    Its  distance  ?     What  is  Prof.  Airy's  remark? 

223.  How  long  would  it  take  light  to  reach  the  nearest  star  ? 
How  would  the  earth's  orbit  appear  at  that  distance  ?    Our 
sun  ?     How  long  does  it  take  for  the  light  of  the  smaller  stars 
to  reach  the  earth  ?     What  can  you  say  of  the  motion  of  the 
fixed  stars?     Illustrate. 

224.  What  proof  have  we  that  the  stars  are  suns ?     ("If 
Sirius  shines  as  brightly  as  our  sun,  at  its  distance,  it  must  be 
three  thousand  times  larger." — LOCKYER.)     That  our  sun  is 
only  a  small  star  ?     Describe  the  motion  of  the  solar  system. 
What  is  the  centre  ?      How  many  stars  can  we  see  with  the 
naked  eye  ?    With  a  telescope  ?     Have  all  the  stars  been  dis- 
covered ? 

226.  What  is  the  cause  of  the  twinkling  of  the  stars  ?     Do 
the  stars  twinkle  in  tropical  regions  ?     Why  not  ?     What  do 
you  say  of  the  magnitude  of  the  stars  ?     Name  four  points 
of  difference  between  a  planet  and  a  fixed  star. 

227.  What  do  you  mean  by  a  star  of  the  first  magnitude  ? 
How   many  are  there  ?      Of  the  second  magnitude  ?      How 
many  sizes  may  one  see  with  the  naked  eye  ?      With  a  tele- 
scope ?     What  is  the  cause  of  the  difference  in  the  brightness 
of  the  stars  ?     What  can  you  say  of  the  names  of  the  stars  ? 

228.  What  can  you  say  with  regard  to  the  division  of  the 
stars  into  constellations  ?     Is  there  any  real  likeness  to  the 
mythological  figures  ?     Name  any  figure  which  seems  to  you 
well  founded. 

229.  Are  the  boundaries  distinct  ?     Who  invented  the  sys- 
tem ?     Give  the  meaning  of  the  signs  of  the  Zodiac  and  their 
origin. 

230.  Explain  why  the  signs  and  constellations  of  the  Zodiac 
do  not  agree. 

231.  What  causes  the  appearance  of  the  constellations? 
Would  they  appear  as  they  now  do,  if  we  should  go  out  into 
space  among  them  ? 

232.  Are  the  present  forms  permanent?     State  the  value  of 
the  stars  in  practical  life. 

233.  What  were  the  views  of  the  ancients  with  regard  to 
the  stars? 


328  QUESTIONS    IN   ASTRONOMY. 

234.  Describe  the  division  of  the  stars  into  three  zones,  and 
name  them. 

THE  CONSTELLATIONS. — The  questions  on  these  are  uni- 
formly :  (i)  description,  (2)  principal  stars,  and  (3)  mythologi- 
cal history.  They  need  not  therefore  be  repeated  with  each 
constellation. — What  are  the  pointers?  Does  Polaris  mark 
the  exact  position  of  the  North  Pole  ?  How  many  times  per 
day  is  Polaris  on  the  meridian  of  any  place  ?  Explain  how 
this  applies  in  navigation  or  surveying.  State  how  the  amount 
of  the  variation  from  the  true  north  will  change  through  the 
ages.  What  star  will  ultimately  become  the  pole-star  ?  What 
curious  facts  are  stated  concerning  the  Pyramids  ?  What  do 
you  say  of  the  distance  of  Polaris  ?  How  may  latitude  be 
calculated  by  means  of  Polaris  ? 

DOUBLE  STARS,  ETC. — Does  any  star  appear  double  to  the 
naked  eye  ?  How  many  have  been  found  by  the  use  of  the 
telescope  ?  What  is  an  optical  double  star  ?  Are  all  double 
stars  of  this  class  ?  Describe  the  revolution  of  a  binary  sys- 
tem. What  other  combinations  have  been  discovered  ?  Their 
periods  ? 

266.  Orbits  ?     Mass  ?    Are  these  companion  stars  as  close 
to  each  other  as  they  seem  ?     What  can  you  say  of  the  colored 
stars  ?     Do  their  colors  ever  change  ?     Which  colors  would  in- 
dicate the  hottest  star  ? 

267.  What  is  the  probable  effect  in  a  system  having  colored 
suns  ?     What  are  variable  stars  ?      Describe  the  changes  of 
Algol. 

268.  Of  Mira.     What  is  the  cause  ?    What  are  temporary 
stars  ?    Describe  the  one  seen  in  Cassiopeia. 

269.  The  one  in  Corona  Borealis,  in  1866.     What  are  lost 
stars  ? 

270.  Can  you  give  any  explanation  ?     Of  what  did  the  star 
of  1866  consist?    Are  these  stars  destroyed?    Is  the  process  of 
creation  now  complete  ? 

271.  What  are  star  clusters  ?    Name  several. 

272.  Is  such  a  grouping  a  mere  optical  effect  ?     Are  they 
probably  as  closely  compacted  as  they  seem  to  be  ?      What 
are  nebulas  ?     How  do  they  differ  from  clusters  ?     Is  it  proba- 
ble that  all  nebulas  will  be  resolved  into  clusters  ?     What  has 
spectrum  analysis  proved  some  of  the  nebulas  to  be  ? 

273.  Are  they  suns?      Where  are   they  most  abundant? 
What  can  you  say  about  their  distances  ?      Into  how  many 
classes  are  they  divided  ?     Describe  and  illustrate  the  elliptic 
nebulae.      What  is  said  of  the  distance  of  the  great  nebula  in 
Andromeda  ?      The  number  of  stars  it  contains  ?      Describe 


QUESTIONS    IN   ASTRONOMY.  329 

the  annular  nebulae.      What  is  said  of  the  "  ring  universe" 
in  Lyra  ? 

276.  Its  diameter?      Describe  the  spiral  nebula  in  Canes 
Venatici.     Describe  the  planetary  nebulas.     What  is  said  of 
the  number  and  size  of  these  "island  universes?" 

277.  Describe   the  fantastic  appearance  of   the  irregular 
nebulae.     What  are  nebulous  stars  ?     What  is  the  cause  ? 

278.  What  is  said  of  the  size  of  the  one  in  Cygnus  ?    What 
are  variable  nebulae  ? 

279.  Give  instances.     What  is  said  of  double  nebulae  ?     Is 
anything  definite  known  with  regard  to  them  ?    What  are  the 
Magellanic  clouds  ? 

280.  Describe  the  Milky-way.     What  can  you  say  of  the 
number  of  stars  in  the  Galaxy  ?    Are  the  stars  uniformly  dis- 
tributed ? 

281.  What  is  HerschePs  theory  of  the  constitution  of  the 
universe  ?     If  this  theory  be  true,  what  is  our  sun  ? 

282.  Give  an  account  of  the  Nebular  hypothesis.     What  is 
said  of  Saturn's  rings  ?     May  they  ultimately  disappear  ? 

284.  What  is  spectrum  analysis  ?    Name  the  three  kinds  of 
spectra. 

285.  What  colored  rays  will  a  flame  absorb  ?    Describe  the 
spectroscope. 

286.  What  are  Fraunhofer's  lines  ?    What  is  known  of  the 
constitution  of  the  sun  ?     What  proof  have  we  that  iron  exists 
in  the  sun  ? 

287.  What  elements  have  been  found  in  the  sun  ?    What 
proof  have  we  that  the  stars  are  suns  ?    What  can  you  say  of 
the  similarity  existing  between  the  stars  and  our  earth  ? 

288.  What  has  been  discovered  with  regard  to  the  constitu- 
tion of  the  Nebulae  ?     Of  their  relative  brightness  ? 

TIME. — What  two  methods  of  measuring  time  ?    What  is  a 
sidereal  day  ? 

289.  What  are  astronomical  clocks?     Tell  how  they  are 
used.     Why  do  astronomers  use  sidereal  time  ?      What  is  a 
solar  day  ?    What  causes  the  difference  between  a  sidereal  and 
a  solar  day  ?    To  how  much  time  is  a  degree  of  space  equal  ? 

290.  Which  is  taken  as  the  unit,  the  solar  or  the  sidereal 
day  ?     How  long  is  a  solar  day  ?     A  sidereal  day  ?     A  solar 
day  equals  how  many  sidereal  hours  ?     A  sidereal  day  equals 
how  many  solar  hours  ?     Describe  mean  solar  time.     What  is 
apparent  noon  ?     Mean  noon  ?    The  equation  of  time  ?    When 
is  this  greatest  ?    When  least  ? 

291.  When  do  mean  and  apparent  time  coincide?     Can  a 
watch  keep  apparent  time  ?     How  may  apparent  time  be  kept? 


330  QUESTIONS    IN   ASTRONOMY. 

How  can  it  be  changed  into  mean  time  ?  Tell  how  to  erect  a 
sun-dial.  When  will  a  sidereal  and  a  mean-time  clock  co- 
incide ?  A  mean-time  clock  and  the  sun-dial  ? 

292.  Give  the  two  reasons  why  the  solar  days  are  of  unequal 
length. 

294.  What  is  the  civil  day  ?     Who  invented  the  present 
division  ?    Describe  the  customs  of  various  nations.     What 
is  the  origin  of  the  names  of  the  days  ?*     What  is  the  sidereal 
year  ?     The  mean  solar  year  ?    What  causes  the  difference  ? 

295.  What  is  the  anomalistic  year  ?    How  did  the  ancients 
find  the  length  of  the  year  ?     What  error  did  they  make  ? 
What  was  the  result  ?     Give  an  account  of  the  Julian  calendar. 
The  Gregorian  calendar.     What  is  the  meaning  of  the  terms 
O.  S.  and  N.  S.  ?     What  country  now  uses  O.  S.  ?     When 
was  the  change  adopted  in  England  ?     How  was  it  received  ? 
How  could  a  child  be  eight  years  old  before  a  return  of  its 
birthday  ? 

297.  When  do  the  Jews  begin  their  year  ?  Why  does  our 
year  begin  January  ist  ?  Show  how  the  earth  is  our  timepiece. 
What  influence  has  Jupiter's  moons  on  the  cotton  trade? 

CELESTIAL  MEASUREMENTS. — These  problems  are  to  be 
used  throughout  the  study.  They  require  no  questions  but 
the  formal  statement  of  the  problem  requiring  solution. 


*  It  is  said  that  the  Egyptians  named  the  seven  days  from  the  seven 
celestial  bodies  then  known.  The  order  was  continued  by  the  Romans. 
Tuesday  they  called  Dies  Mortis ;  Wednesday,  Dies  Mercurii  ,•  Thursday, 
Dies  Jovis ;  Friday,  Dies  f^eneris.  In  the  Saxon  mythology,  Tius,  Wo- 
den, Thor,  and  Friga  are  equivalent  to  Mars,  Mercury,  Jupiter,  and 
Venus.  Hence  we  see  the  origin  of  our  English  names. 


GUIDE  TO  THE  CONSTELLATIONS. 


THE  following  is  a  description  of  the  appearance  of  the  heavens  on  or  about 
the  first  day  of  each  month  in  the  year. 

January.  (7  p.  M.)— ~ In  the  North,  Cassiopeia  and  Per- 
seus are  above  Polaris,  Cepheus  and  Draco  west,  Ursa  Minor 
below,  and  Ursa  Major  below  and  to  the  east.  In  the  East, 
Cancer  is  just  rising,  Canis  Minor  (Procyon)  has  just  risen. 
Along  the  Ecliptic,  Gemini  is  well  up,  then  Taurus,  Aries 
reaches  to  the  meridian,  next  Pisces,  Aquarius  (letter  Y)  and 
Capricornus  just  setting.  In  the  Southeast,  Orion  and  the 
Hare  are  well  up.  In  the  South,  Cetus  swims  his  huge  bulk 
far  to  the  east  and  west.  In  the  Southwest  is  Piscis  Australis 
(Fomalhaut).  North  of  the  Ecliptic  the  Triangles  are  nearly 
in  the  zenith,  Perseus  is  just  east,  below  is  Auriga,  Androme- 
da lies  just  west  of  the  meridian,  and  Pegasus  is  midway,  while 
Delphinus  (the  Dolphin,  Job's  Coffin),  Aquila  (Altair),  and 
Lyra  (Vega)  are  fast  sinking  to  the  western  horizon. 

February.  (7  p.  M.) — In  the  North,  Ursa  Major  lies 
east  of  Polaris,  Ursa  Minor  and  Draco  below,  Cepheus  west, 
Cassiopeia  above  and  to  the  west.  In  the  East,  Regulus  and 
Cor  Hydrae  are  just  rising.  Along  the  Ecliptic,  Leo  (Regulus, 
the  sickle)  just  rising,  Cancer  well  up,  Gemini  midway,  Taurus 
on  the  meridian,  Aries  (the  scalene  triangle)  past,  Pisces 
next,  and  lastly  Aquarius  just  setting.  In  the  Southeast, 
Canis  Minor,  Canis  Major  (Sirius),  and  Orion  are  conspicuous. 
In  the  Southwest,  Cetus  covers  nearly  the  whole  sky.  North 
of  the  Ecliptic,  Perseus  is  on  the  meridian,  while  Auriga  is  a 
little  east  of  it ;  west  of  Perseus  is  Andromeda,  while  the  great 
square  of  Pegasus  is  fast  approaching  the  horizon. 

march.  (7  p.  M.)— In  the  North,  Ursa  Major  lies  east 
of  Polaris,  Draco  and  Ursa  Minor  below,  Cepheus  below  and 
to  the  west,  and  Cassiopeia  west.  In  the  East,  Cor  Caroli 
(the  Greyhound)  is  well  up,  and  Coma  Berenices  is  rising. 
Along  the  Ecliptic,  Leo  is  fully  risen,  next  Cancer,  Gemini 
reaches  to  the  meridian,  Taurus  is  past,  Aries  midway,  and 
lastly  Pisces  is  just  beginning  to  set.  In  the  Southeast,  Cor 


332  GUIDE  TO  THE  CONSTELLATIONS. 

Hydrae,  Canis  Minor  and  Canis  Major  are  conspicuous.  In  (he 
South,  Orion  blazes  brilliantly.  In  the  Southwest,  Cetus  is 
hiding  below  the  horizon.  North  of  the  Ecliptic,  Auriga  is  in 
the  zenith  ;  west  are  Perseus  and  Andromeda,  while  Pegasus 
is  just  beginning  to  sink  out  of  sight. 

April.  (7  p.  M.) — In  the  North,  Ursa  Major  is  above  and 
to  the  east  of  Polaris ;  opposite  and  to  the  west  is  Perseus, 
Draco  below  and  to  the  east,  Cepheus  below  and  to  the  west, 
Cassiopeia  west.  In  the  East,  Bootes  ( Arcturus)  not  quite  fully 
risen.  Along  the  Ecliptic,  Virgo  (Spica)  rising,  Leo  midway, 
Cancer  reaches  to  the  meridian,  Gemini  past,  next  Taurus, 
then  Aries,  and  lastly  Pisces  just  setting.  In  the  Southeast  is 
the  Crater  (the  Cup),  and  Hydra  stretches  its  long  neck  to  the 
meridian.  In  the  South,  Canis  Minor.  In  the  Southwest, 
Sirius  and  Orion.  North  of  the  Ecliptic,  and  in  the  northeast, 
are  Coma  Berenices  and  Cor  Caroli ;  above  Gemini  and  Taurus 
is  Auriga,  while  Andromeda  is  just  setting  in  the  northwest. 

May.  (8  P.  M.) — In  the  North,  Ursa  Major  is  above  Polaris, 
Ursa  Minor  and  Draco  east,  Cepheus  and  Cassiopeia  below, 
and  Perseus  west.  In  the  East,  Lyra  is  just  rising,  and  Her- 
cules is  just  up.  Along  the  Ecliptic,  Libra  is  just  rising,  Virgo 
is  midway,  Leo  is  on  the  meridian,  Cancer  is  past,  next  Gemini, 
and  lastly  Taurus  just  setting.  In  the  South,  stretching  east 
and  west  of  the  meridian,  is  Hydra,  with  the  Crater  and  Cor- 
vus  a  little  east.  In  the  Southwest,  is  Cor  Hydras,  Canis  Major, 
and  Canis  Minor,  while  Orion  is  just  setting  in  the  west.  North 
of  the  Ecliptic,  in  the  east,  above  Hercules,  are  Corona  Bore- 
alis  (The  Northern  Crown),  Bootes  (Arcturus),  Coma  Bere- 
nices, and  Cor  Caroli,  which  stretch  nearly  to  the  meridian.  In 
the  Northwest,  above  Taurus  and  Perseus,  is  Auriga. 

June.  (8  P.  M.)— In  the  North,  Ursa  Major  is  above  Po- 
laris, Draco  and  Ursa  Minor  to  the  east,  Cepheus  below  and 
to  the  east,  and  Cassiopeia  directly  below.  In  the  East,  Cyg- 
nus  and  Aquila  are  just  rising,  Lyra  and  Taurus  Poniatowskii 
are  well  up.  Along  the  Ecliptic,  Scorpio  is  rising,  Libra  is  mid- 
way, Virgo  on  the  meridian,  Leo  past,  Cancer  midway, 
Gemini  next,  and  Taurus  just  setting.  In  the  South  are  Cor- 
vus  and  the  Crater,  a  little  past  the  meridian.  In  the  South- 
west is  Cor  Hydras,  and  in  the  west  Canis  Minor  approaching 
the  horizon.  North  of  the  Ecliptic,  in  the  east,  above  Scorpio, 
is  Hercules ;  then  Corona  and  Bootes,  and  near  the  meridian, 
Cor  Caroli  and  Coma  Berenices.  In  the  Northwest  is  Auriga, 
just  coming  to  the  horizon. 

July.   (9  p.  M.)— In  the  North,  Draco  and  Ursa  Minor 


GUIDE  TO  THE  CONSTELLATIONS.  333 

above  Polaris,  Ursa  Major  west,  Cepheus  east,  and  Cassi- 
opeia below  to  the  east.  In  the  East,  the  Dolphin  (Job's 
Coffin)  is  row  well  up,  Cygnus  is  almost  midway  to  the  me- 
ridian, and  Lyra  is  still  higher.  Along  the  Ecliptic,  Capri- 
cornus  is  rising,  Sagittarius  (the  Archer)  is  next,  Scorpio,  with 
its  long  tail  swinging  along  the  horizon,  is  directly  south, 
Libra  is  past  the  meridian,  Virgo  midway,  and  Leo  has  almost 
reached  the  horizon.  In  the  Southwest,  the  Crater  is  setting, 
and  Corv-us  is  just  above.  North  of  the  Ecliptic,  above  Scorpio 
and  east  of  the  meridian,  are  Serpentarius,  Hercules,  and 
Taurus  Poniatowskii ;  Corona  is  almost  on  the  meridian,  to 
the  west  of  which  lie  Bootes,  Cor  Caroli,  and  Coma  Berenices. 

August.  (9  P.  M.) — In  the  North,  Draco  and  Ursa  Minor 
are  above  Polaris,  Cepheus  above  and  to  the  east,  Cassiopeia 
east,  and  Ursa  Major  west.  In  the  Northeast,  Perseus  is  just 
rising,  while  south  of  it  Andromeda  and  Pegasus  are  fairly 
up.  Along  the  Ecliptic,  Aquarius  is  risen,  next  Capricornus, 
Sagittarius  reaches  to  the  meridian,  Scorpio  is  just  past,  Libra 
next,  and  Virgo  (Spica)  just  touches  the  horizon.  North  of 
the  Ecliptic,  Taurus  Poniatowskii  is  on  and  Lyra  is  just  east  of 
the  meridian ;  the  Swan  and  Dolphin  are  east  of  Lyra,  Ser- 
pentarius and  Hercules  are  above  Scorpio,  and  just  west  of 
the  meridian  ;  thence  west  are  Corona  and  Bootes,  while  far 
in  the  northwest  are  Coma  Berenices  and  Cor  Caroli. 

September.  (8  p.  M.) — Draco  is  above  and  to  the  west 
of  Polaris,  Cepheus  above  and  to  the  east,  Cassiopeia  east, 
Ursa  Major  is  below  and'to  the  west.  In  the  Northeast,  Per- 
seus is  just  rising.  In  the  East,  Andromeda  is  fairly  up,  Peg- 
asus is  nearly  midway  to  the  meridian.  Along  the  Ecliptic, 
Pisces  is  just  rising,  next  Aquarius,  Capricornus  in  the  south- 
west, Sagittarius  on  the  meridian  in  the  south,  next  Scorpio 
in  the  southwest,  Libra,  and  lastly  Virgo  just  setting.  North 
vfthe  Ecliptic,  Lyra  is  on  the  meridian,  Cygnus,  the  Dolphin, 
and  Aquila  just  to  the  east,  while  to  the  west  are  Taurus 
Poniatowskii  and  Serpentarius;  north  of  these  latter  are  Her- 
cules, Corona,  Bootes,  Cor  Caroli,  and  Coma  Berenices. 

October.  (7  p.  M.) — In  the  North,  Cepheus  and  Draco 
are  above  Polaris,  Ursa  Minor  west,  Cassiopeia  east,  and  Ursa 
Major  below  and  west.  In  the  Northeast,  Perseus  is  fairly 
risen.  In  the  East,  Andromeda  is  nearly  midway  to  the  ze- 
nith. Along  the  Ecliptic,  Aries  is  just  rising,  Pisces  well-  up, 
Aquarius  and  Capricornus  in  the  southeast,  Sagittarius  in 
the  south,  Scorpio  far  down  in  the  southwest,  and  Libra  just 
/settin g.  North  of  the  Ecliptic,  Cygnus  and  Aquila  are  on  the 


834  GUIDE  TO  THE  CONSTELLATIONS. 

meridian,  the  Dolphin  just  east  of  it,  and  far  south ;  Lyra  is 
west  of  the  meridian,  Taurus  Poniatowskii  lower  down  and  to 
the  south,  Serpentarius  is  just  above  Scorpio ;  next,  in  line 
with  it  and  Polaris,  is  Hercules ;  Corona  and  Bootes  are  toward 
the  northwest,  where  Coma  Berenices  is  just  setting. 

November.  (7  p.  M.) — In  the  North,  Ursa  Major  is  below 
Polaris,  Ursa  Minor  and  Draco  are  to  the  west,  Cepheus 
above,  and  Cassiopeia  above  and  to  the  east.  In  the  North- 
east, Auriga  is  just  rising,  and  Perseus  is  above,  nearly  mid- 
way to  the  meridian.  Along  the  Ecliptic,  Taurus  is  just  rising, 
next  Aries  and  Pisces ;  Aquarius  is  on  the  meridian,  south ; 
then  Capricornus,  and  lastly  Sagittarius,  in  the  southwest. 
North  of  the  Ecliptic,  Pegasus  and  Andromeda  lie  east  of  the 
meridian,  the  Swan,  Dolphin,  Eagle,  Taurus  Poniatowskii,  and 
Lyra  west.  In  the  Northwest  are  Hercules  and  Corona. 

December.  (7  p.  M.)— In  the  North,  Cassiopeia  is  above 
Polaris,  Cepheus  above  and  to  the  west,  Perseus  above  and 
to  the  east,  Draco  west,  and  Ursa  Major  below.  In  the 
Northeast,  below  Perseus,  is  Auriga.  In  the  East,  Orion  is 
rising.  Along  the  Ecliptic,  Gemini  is  just  rising,  Taurus  is 
nearly  midway,  next  Aries,  Pisces  is  on  the  meridian,  then 
Aquarius,  and  lastly  Capricornus,  far  in  the  southwest.  In  the 
South,  east  of  the  meridian,  is  Cetus,  and  west  is  Fomalhaut. 
North  of  the  Ecliptic,  Andromeda  is  nearly  on  the  meridian, 
and  Pegasus  west  of  it;  Cygnus,  Delphinus,  Lyra,  and  Aquila 
are  about  midway,  while  Taurus  Poniatowskii  is  just  sinking  to 
the  horizon.  In  the  Northwest,  Hercules  is  just  setting. 

NOTE.— It  should  be  borne  in  mind  that  a  month  makes  a  variation  of 
about  two  hours  (30°)  in  the  rise  of  a  star :  hence,  in  the  foregoing  "  Guide," 
the  "January  Sky1'  of  9 p.  M.  would  be  about  the  same  as  the  "February 
Sky"  of  7  P.  M.  ;  the  "January  Sky"  of  11  P.  M.  would  be  about  the  same  as 
the  "March  Sky"  of  7  P.  M.,  &c.  In  this  way  the  "Guide"  may  be  used  for 
any  hour  in  the  night.  The  pupil  will  see  that  in  the  "  Guide"  the  prominent 
figures  and  stars  in  each  constellation  are  given  in  parentheses.  Examples : 
the  "  Y"  in  Aquarius,  the  "  scalene  triangle"  in  Aries.  "  Job's  coffin"  iu  the 
Dolphin,  "  Procyon"  in  Canis  Minor,  &c.  These  aid  in  identifying  the  con- 
stellation. 


INDEX. 


PAGE 

Aberration 136 

Aerolites 195 

Algol 243 

Aldebaran 247 

Amplitude 37 

Antinous 261 

Anaxagoras 17 

Andromeda 245 

Antares 260 

Apsides 128 

Apparent  motion 99 

Arcturus 256 

Argo  264 

Arcturus 256 

Aries 246 

Auriga 248 

Azimuth 37 

Astrology 22 

Daily's    Beads 159 

Bellatrix 251 

Betelgeuse 251 

Bode'sLaw _ 173 

Bolides 196 

Bootes 256 

Berenice's  Hair 255 

Cassiopeia 241 

Cams  Major,  Canis  Minor 252 

Cancer 254 

Capricornus 261 

Castor  and  Pollux 250 

Celestial  Sphere 35 

"       Pole 38 

"       Measurements 38 

"       Chemistry 284 

Centanr 264 

Cepheus 241 

Cetus 249 

Chinese  26 

Chaldeans 17 

Colures 40 

Conjunctions 71,  75 

CorCaroli 255 

Corona. 259 

Comets 206 

Constellations 234 

Copernican  System 23 

Cross 264 

Crystalline  Spheres 18 

Cygnus 262 


Declination 

Dipper 

Diurnal  Motion. 

Dolphin. 

Draco 


100 


Earth  96 

Earth-shine 144 

Eclipses 155 

Ecliptic 40,  109 

r'       Potesof .      41 


Ecliptic,  Obliquity  of. 110 

Egyptians 19 

Ellipse 68,  26 

Elongation 76 

(Measurements; 298 

Emersion 181 

Equinoxes- 113 

"       Precession  of 121 

Equinoctial 38 

Evening  Stars 82 

Falling  Stars „.  195 

Fixed  Stars 222 

44         Names  of 227 

"         Distance  of.....                   ..  223 

"         Motion  of 223 

"         Size  of. 226 

44         Parallaxof 223 

Galileo....                               29 

Galaxy 280 

Gemini 249 

Geocentric 75 

Gibbous 146 

Golden  Number 162 

Greek  Alphabet 228 

Grecians 17 

Gravitation 34 

Harvest  Moon 148 

Hare 251 

Hercules 257 

Herschel's  Theory 281 

Heliocentric 75 

Horizon 37 

Hour  Circles 38 

Hyades 247 

Hydra 255 

Immersion '. 181 

Irradiation 141 

Job's  Coffin....                                     ..  252 

Jupiter 175 

Kepler's  Laws * 25 

KirchofiTs  Theory 61 

Latitude ...  .41 

LeMonnier 190 

Le  Verrier 193 

Leo 253 

Libra 260 

Linniens 152 

Librations : 142 

Lyra 263 

Mars .  168 

Meteors 194 

Mean  day 293 

Mercury 83 

Metonic  Cycle 161 

Milky  War 280 


336 


INDEX. 


FAGS 

Minor  Planets 172 

Moon 139 

"  Eclipseof. 162 

Na<Hr 37 

Naos 252 

Newton 31 

Nebular  Hypothesis 282 

Nebube 272 

Neptune 191 

Noon-mark 291 

North  PolarStar. 237 

Nodes 69,149 

11  Longitude 69 

'  Line  of. 69 

Orbits  of  Planets 66 

"  Stars 104 

Occultntion 149 

Orion 251 

Parallax...                                            ,.  137 

ofstars 222 

Penumbra 155 

PerseuK 243 

Pegasus 245 

Pisces 248 

Phases 78 

Planet* 65 

Pleiades 247 

Polaris 237 

PolarSiar 237 

"    Stars,  South 56,106 

"    (L  stance 39 

Procyon 252 

Precession 120 

Ptolemaic  Theory 20 

Pythagoras 18 


Quadrature  , 


76 

Refraction 130 

Retrograde  motion 77.  79 

Reprulus  253 

Right  ascension 39 


Saros 160 

Saturn 182 

Sagittarius 261 

Scorpio 260 

Scintillation 226 

Signs  of  Zodiac 42,  230 

Seobcoa .  110 


Serpentarins 2.r»9 

Shooting  Stars 194 

Sirius 252 

Sidereal  Revolution 55,  80 

Southern  Fish 261 

Solstices 41,  114 

Solar  time 289 

Solar  System < 45 

Spectrum  Analysis 2S4 

Spica 254 

Sun 43 

"    Pathof 108 

"    Change  in  form  and  place  of. 131 

"    Spots 5C 

Stars 221 

"    Numberof. 224 

"    Size 226 

"    Distance 223 

"    Colored 266 

"    Variable ..  267 


Temporary, 
auble 


Double 265 

Syzygies 166 

Synodic 55,  80 


Taurus 247 

"       Poniatowskii 860 

Tides 165 

Time 288 

Transit 77 

Triangles 246 

Tycho  Brahe 24 

Twilight ; 133 

Umbra 155 

Uranus 189 

Ursa  Major 235 

"    Minor. 237 

..  262 


Vega 

Venus 

Vertical  Circle 37 

Velocity  of  Light 182 

Virgo 254 

Vnlcan 82 

Whale 249 

Wilson's  Theory 62 

Zenith 87 

Zodiac 41 

Zodiacal  Light 217 


14 


"FOURTEEN  WEEKS "  H  HTUML  SCIENCE. 

IEIP    TREATISE    IN    EA.CH    IBJEt 

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Davies'  Shades,  Shadows,  and  Perspective.— A  succinct  exposition  of 
the  mathematical  principles  involved. 

Davies'  Science  of  Mathematics-— For  teachers,  embracing 

I.  GRAMMAR  OP  ARITHMETIC,  III.  LOGIC  AND  UTELITT  OF  MATHEMATICS, 

n.  OUTLINES  OP  MATHEMATICS,          IV.  MATHEMATICAL  DICTIONARY. 


KEYS  MAT  BE  OBTAINED  FROM  THE  PUBLISHERS 

BY   TEACHERS   OHtY. 


*w,  alt  paimtni,  aud  all 


NATIONAL     TTTQTfVB'V"    STANMRD 

SERIES.        11X01  UHJL»   TEXT-BOOKS. 


"History  is  (Philosophy  teaching  by  Examples!'" 


THF    IINITFD    STftTF^        »•  Youth's   History  of  the 

i  nt  um  i  tu  o  i  A  i  no.      ^^  STATEj  ByjAME8 

MONTBITH,  author  of  the  National  Geographical  Series.  An  elementary  work 
upon  the  catechetical  plan,  with  Maps,  Engravings,  Memofiter  Tables,  etc.  For 
the  youngest  pupils. 

2,    Wlllard's    School    History,   for  Grammar  Schools  and  Academic  classes. 
Desip™«*i  *«  <*"Hivate  the  memory,  the  intellect,  and  the  taste,  and  to  BOW  the 


921232 


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2.    Si 

THE  UNIVERSITY  OF  CALIFORNIA  LIBRARY 

D fl lUfF RlCOrd's  History  of  Rome.    A  story-like  epitome  of  this  inter- 
1 1  w  If  I  !•  •        eating  and  chivalrous  history,  •orofusely  illustrated,  with  the  legends 

and  doubtful  portions  so  introduced  as  Lot  to  deceive,  while  adding  extended 

charm  to  the  subject. 

RFNFRAI        Wi  I  lard's  Universal   History.    A  vast  subject  BO  arranged 
U 1.  II L.  I IH  L.  •  aD<i  illustrated  as  to  be  less  difficult  to  acquire  or  retain.  Its 

whole  substance,  in  fact,  is  summarized  on  one  page,  in  a  grand  "  Temple  of 

Time,  or  Picture  of  Nations. 

2  General  Summary  of  History.  Eeing  the  Summaries  of  American,  and 
of  English  and  Erench  History,  bound  in  one  volume.  The  leading  events  in 
the  histories  of  these  three  nations  epitomized  in  the  briefest  manner. 


A.   S.   BARNES   &  CO.. 


